When Mayor Bloomberg announced this morning that he will prevent teacher layoffs by freezing wages, teachers union president Michael Mulgrew shot back that the mayor can’t unilaterally make contract decisions.

Mulgrew is right that Bloomberg can’t make teachers contract decisions on his own. But in this case, he doesn’t have to. All Bloomberg has to do to freeze wages is not sign any contract that includes a raise.

The teachers union is left with a decision: it can either agree to a contract with no raises, or not. If the city and union are unable to come to an agreement, teachers can continue working under the old contract indefinitely.

But speaking to reporters today, Schools Chancellor Joel Klein also made it clear that the city is open to discussing alternate deals with the union. The city’s contract negotiation wish-list includes a slew of cost-saving measures that the city could be willing to trade for raises. These include firing excessed teachers who have not found new positions after six months or a year, or requiring that teachers work longer hours.

In an interview today, Mulgrew refused to say whether he was considering agreeing to a contract without raises. “In terms of our negotiation process, nothing has changed,” he said.

Mulgrew emphasized that a number of variables, including the months-overdue state budget, could affect whether or not the city is eventually able to afford 2 percent pay raises for teachers.

This type of maneuvering on the city’s part would not be possible with other municipal unions. The city’s negotiations with the teachers union have been stalled for months and are headed to arbitration. For some unions, arbitrators’ recommendations are binding. But for the UFT, neither side is obliged to follow the recommendations of independent fact-finders.