The Metropolitan Opera postponed a threatened lockout late on Thursday night, saying that it had done so at the request of a federal mediator who was brought in at the 11th hour to try to salvage its contract negotiations with the unions representing its orchestra and chorus.

With management granting a 72-hour reprieve to try to reach agreements with the unions, though, it was still unclear if the lockout had been averted, or merely delayed. While opening night for the new season is not until Sept. 22, a lockout would stop rehearsals that are already underway.

The Met’s general manager, Peter Gelb, had threatened to lock out the company’s employees if progress was not made toward new labor agreements before the contracts for 15 of its unions expired at midnight. But on Thursday morning the unions representing the orchestra and chorus agreed to his proposal to bring in a federal mediator, and after some late-night talks at the opera house, Mr. Gelb agreed to let talks continue.

“At the Federal Mediation and Conciliation Service’s request, we’ve agreed to extend the deadline for 72 hours so we can have a chance to see if we can reach an agreement,” he said in an interview late Thursday night. “If they want to make a deal with us, and we hope to make a deal with them, the next 72 hours should give us ample time to do it.”