The theater actors’ union said on Monday that it was barring its members from taking part in developmental work on Broadway shows while it demands a new contract that includes some profit-sharing.

The union, Actors’ Equity, called the action a strike, and said it would take effect immediately, preventing its members from working on developmental labs, workshops and staged readings. About a quarter of all Broadway shows use developmental labs to test out material, and there are several labs scheduled in coming months that will not take place unless the dispute is settled.

“No union wants to get to this point, but we feel strongly because our members feel strongly,” Kate Shindle, the union president, said. “Our members who do this work don’t think the terms are fair.”

The Broadway League, representing producers, said it was still hopeful that the dispute would be resolved. “The Broadway League has been negotiating in good faith over multiple sessions and there are additional proposals to make,” the trade group said in a statement. “We look forward to continuing our respectful dialogue with the union and are confident that we will reach a fair agreement that will be beneficial to both sides.”