When productions transfer from the West End to Broadway (or vice versa), the theatre community is often abuzz with speculation as to who will star. Will the original lead replicate their performance to great acclaim? Will a newcomer step in? While the word "transfer" implies a one-to-one comparison, it is exceedingly rare for a full transfer to take place. The majority of transfer productions—such as Leopoldstadt, Bad Cinderella, or Six on Broadway (or Hamilton and Pretty Woman on the West End)—select new cast members for the new market.

The reason? The actors unions in the United States and the United Kingdom may both be titled Equity, but they aren't exactly equal.

The trade unions, which were formed independent of each other in the first half of the 20th century, have developed a semi-symbiotic relationship over the intervening century. With Broadway and the West End serving as their respective leaders for commercial theatre success, both Actors' Equity (US) and Equity (UK) have repeatedly reached agreements to transfer productions from one shore to the other. Most of the time, these transfers occur with the original artists intact, though there have been some very notable exceptions and conflict in the process. Both British and American artistic invasions have occurred several times on both shores, and as the gap between the two theatre communities continues to thin with the advent of the internet, demand for productions to hop the pond has only increased.

But when a production hops the pond, it's not a guarantee that the actors will come along for the ride.

As the unions are symbiotic, and not directly connected, the chess board of decisions involved in a transfer can easily be upended by trade negotiations between the unions. When unions are directly connected, these negotiations are much smoother; Actors Equity and the Screen Actors Guild are considered sister unions, and if a member joins one union, they are automatically eligible to join the other union.

The same is not true of Actors Equity and Equity. Both unions maintain their own separate list of members, and requirements for membership. Notably, you cannot be a member of both unions; while you can feasibly work in both markets, you have to select one as your home base due to citizenship requirements, and then apply for work visas to engage with the other market.

The entire process is not unlike the trading of players that happens between sports teams, only instead of an entire league to balance, there are two teams facing off time and again, both of whom are trying to protect their home advantage (and trying to get more work for their actors).

In the first century of musical theatre history, this was not much of a problem. While a play might hop the pond, it was rare for performers to go with it, as stage actors in one market were not necessarily stars in the opposite market. Fame was much more localized in the first half of the 20th century; unless a performer reached the status of screen star or musical marvel, international demand was not a built-in aspect of celebrity. For actors that had reached that level of celebrity, accommodations could be somewhat easily made—as the acceptance of one or two international actors a season was an easily incorporated aspect for the production and the unions. 

By the mid-century, however, celebrity started changing.

The intense proliferation of cast recordings, coupled with greater photo and video recording quality, made it possible for stage stars to shine for theatre lovers across the world. Performances were captured, and when the production transferred, audiences began to expect the performer to come along—with the show and star becoming synonymous in select cases. Just as the pop music world shifted to become celebrity focused, with performers coming to "own" certain songs in the eyes of the public, so did some actors come to "own" certain roles.

Naturally, this led to union tensions. If performers didn't have a chance to audition for the original cast of a production originating on the other side of the ocean, was it fair to also rob them of the chance of participating in the production in their home market? 

From here on out, the history of trading performers is examined from the Actors' Equity side of the deal.

Two specific types of actor trades are available: international stars, who are supported by fan bases on both sides of the pond, and a unique service performer, who is carrying out a role that no other performer in the market is able to perform.

This second option is much more difficult to achieve. Producers must prove beyond the shadow of doubt that they have exhaustively searched the American market, only to come up empty. A production team cannot declare a performer uniquely capable without demonstrating that there is no one in the United States equally capable as their chosen performer. And nine times out of 10, roles are not so strenuously specific as to prevent all but one member of humanity from being up to the challenge (otherwise replacements could never happen).

Additionally, there are two types of allowances: unit companies, where a small repertory ensemble serve as both the creative team and cast, such as Mischief (responsible for the upcoming Peter Pan Goes Wrong), and "plays of special character"—a proviso typically utilized for performances that are inseparably tied to an international performer, such as Gabriel Byrne's autobiographical solo show Walking With Ghosts.

Tensions between the UK and the US unions began to simmer in the 1980s, with producer Cameron Mackintosh leading the charge. In 1987, Actors' Equity declined the trade request for Sarah Brightman to originate the role of Christine in The Phantom of the Opera on Broadway—a role she had originated on the West End. The American union declared that a suitable soprano was readily available from the pool of American actors. 

The Broadway production was nearly called off until Mackintosh, Andrew Lloyd Webber, and both unions reached a compromise: Brightman would be allowed to bring the role to New York, but an American actress had to star in Lloyd Webber's next London musical. As a sign of good faith, Mackintosh and Lloyd Webber cast both of the leading female roles in his next musical, Aspects of Love, with American actresses (Kathleen Rowe McAllen and Ann Crumb), keeping them on when the production transferred to Broadway to balance the two non-American leading men. 

By 1990, however, Mackintosh and Actors Equity were in an all-out war of attrition over Miss Saigon. Initially, when Mackintosh had requested an international star trade for Jonathan Pryce to originate the role of The Engineer, who is half-Vietnamese, Actors' Equity firmly declined the request. They stated that the role was crucial to improving employment opportunities for racial minorities in the American theatre, and that as a union they could not condone the casting of a Caucasian actor as a Eurasian character. Not to mention that Pryce's casting in the role led to protests by Asian American artists in the US, notably including David Henry Hwang and BD Wong.

Instead of adhering to the unions guidance, Mackintosh cancelled the production altogether, pressuring Actors' Equity to reverse their decision and allow Pryce to perform. As part of his agreement to continue producing the production, he insisted on being allowed to free cast the production without union involvement. After bitter negotiations, an agreement was reached that allowed Mackintosh to hire two non-American Asian actors for the production, but the union explicitly excluded Lea Salonga from that proviso. Instead, Mackintosh was told that he would have to apply for a unique services permit for her to perform. Unlike with Phantom, a one-for-one trade was not an option, as Salonga (who was from the Philippines) was not a British citizen.

When Mackintosh insisted on Salonga as Kim, this led to another protest. While no one doubted the immense talent Salonga had, Asian American actors across the country resisted Mackintosh's claim that he couldn't find a single Asian actress in the United States that was capable of playing the role. Mackintosh became the bullseye of industry wide anger, with press coverage of the stand off becoming front page news across the industry. After an extended back-and-forth, Salonga was permitted to perform, but tensions between the union and the producer remained for well over a decade.

In 1999, Actors Equity denied the London cast of Mackintosh's Oklahoma, instructing him that the production would have to be fully recast in order to transfer to Broadway. The union remained firm after several years of Mackintosh pushing against the ruling, until he eventually brought the production (with an entirely American cast) to Broadway in 2002.

The American and the British actors' unions came to head in 1999, as well, with Equity calling Actors Equity capricious in a council report that lead to a heated public exchange between the unions. By the millenium, the unions had taken their debates behind closed doors, with only the occasional disagreement reaching the public's ears.

Nowadays, these trades are often considered before talk of a production transferring even begins. For example, when Life of Pi came to Broadway, it was quickly determined that the British puppeteers would come with the production. The reason? Their skillset at operating the specifics of the constructed animals were considered a unique service (so unique that the puppeteers all won a joint Olivier for their work in the show). Outside of the unique service clause, productions can still petition the union to allow for specific performers to come along, as Life of Pi did to bring their additional star, the show's lead Hiran Abeysekera (who won an Olivier for his performance as Pi).

In the majority of cases, however, producers begin the transfer process with the knowledge that they will be casting a new company in the United States, such as & Juliet—the show chose to petition for only one British cast member, Melanie La Barrie, to come across the pond. This allows productions to prove their viability regardless of specific star power, in addition to allowing a new community of performers a chance to dive into the material. And it allows the show to continue playing on the West End with its original cast, while making its mark on Broadway with a new cast.

As both unions continue to adjust their allowances, trade decisions will continue to evolve. As always, audience demand drives change in the commercial market. Who knows! Maybe both Equity's will parse out an international sister union agreement in the future, which can allow for performers to be in both unions. For now, the never-ending actors' chess game continues.