LONDON -- The players' union says the Tampa Bay Rays would need its permission to play games in Montreal.

Commissioner Rob Manfred said last week the low-drawing Rays may explore a split season in Montreal. No timetable for the possible plan was announced

"There is a lot of work that is going to need to be done before that consideration becomes closer to a reality," union head Tony Clark said Friday as the New York Yankees took batting practice at London's Olympic Stadium, a day before playing Boston in baseball's first major league game in Europe. "We look forward to being a part of that conversation, as well. A lot of challenges there."

Clark said requiring a player to maintain two homes during the season would be a "significant burden."

The Montreal Expos were in the National League from 1969 to 2004 before moving to Washington and becoming the Nationals. In their last two seasons before moving, the Expos played 22 games a year in Puerto Rico.

Clark said the union considers a team playing home games in two locations to be a mandatory topic of bargaining under the National Labor Relations Act, making it subject to union agreement.

"Interesting spot that it's in," Clark said. "Interesting idea."

Major League Baseball questions such an interpretation of the NLRA.

"I believe that under the NLRA there is no obligation to bargain over the decision itself, which is a management prerogative, but an obligation to bargain over the effects of the decision on terms and conditions of employment," MLB deputy commissioner Dan Halem said in an email. "It's akin to plant relocation."