New York City’s powerful union leaders are preparing an offensive to fight Gov. Cuomo’s plan to impose a 2 percent cap on binding-arbitration awards they fear could limit salary increases, The Post has learned.

Under current law, the state requires binding arbitration when municipalities reach a contract-talk impasse with their law-enforcement unions. Municipal officials have long complained the awards have been too generous to the unions.

Aides to Cuomo insist the city would be exempt because the proposal applies only to “financially distressed” municipalities subject to the state’s 2 percent property tax cap — which the city isn’t subject to.

But a source briefed on talks with the governor’s office said local labor leaders aren’t buying that.

“New York could be lumped in [down the road],” said the source. “We don’t know.”

The source said the unions might be willing to support an explicit carve-out of New York City in the proposal.