Broadway producers locked in a negotiations impasse with the Rialto stagehands union are getting tough.

The producers are implementing some of the terms of their last, best offer without the agreement of the union, Local One.

The move, set to take effect Monday, is one step short of initiating a lockout of the union, which would darken the majority of Broadway shows. This tactic instead puts the ball in Local One’s court — a potential provocation for the union to call a strike.

“We are forced to implement because Local One will not pursue meaningful change,” said Charlotte St. Martin, exec director of the League of American Theater and Producers, in a statement.

Local One prexy James J. Claffey Jr., said he learned of the producers’ decision from Gotham mayor Michael Bloomberg, adding that he declined an offer from the mayor’s office to help resolve the situation.

“Right now we have to prepare ourselves for any possibility,” Claffey said. “We’re still resolved to try to bargain. We will only consider a strike if we believe it’s the last possible action.”

Claffey said he would not extend an invitation to meet with producers, but would accept one if it came from the other side of the table.

The union cannot strike before a Local One membership meeting Sunday, when a vote to authorize a work stoppage is planned.

Questions have been raised regarding whether the international head of IATSE, the stagehands umbrella org, would sign off on a strike.

But Claffey dismissed those concerns. “I’m expecting the support (the international president of IATSE) has shown us in the past,” he said.