For more than three years, Nutter and D.C. 33 have been unable to work out a new contract.
In mid-January, Nutter said he presented his finally offer to the union after the two sides reached an impasse.
The union rejected that offer, Nutter said. So, on Friday, he announced he would go to court to seek the authority to force the union to take the deal.
"Rather than going ahead and implementing this final offer, and having our hard-working city employees in a state of uncertainty about their compensation, benefits and work rules, we're going to ask the courts to decide on that part of the matter," Nutter said.
The plan the mayor wants to impose incremental pay raises in exchange for cuts in healthcare and overtime rules, reforms in the pension plan and opening the door to possible worker furloughs.
"The deadlock has gone on long enough. Union leaders have held our public employees and the taxpayers hostage to their 'just say no' campaign," Nutter said.
The leaders of the unions say the mayor's deal is not as sweet as he claims, and furloughs are out of the question.
"When is a raise not a raise? When you look at what the city's offering, the wages that they're offering, with what they want to take away that so-called two percent ends up as a six to eight percent deduction," said Pete Matthews of DC 33.
Matthews says he is willing to continue negotiations, even as union lawyers prepare for a court fight.
"It's the same dictatorial attitude that he has about everything. That's how he is," Matthews said. "Do our members deserve a raise? Absolutely. But they don't deserve a minus on their checks."
The court fight could go all the way to the state Supreme Court.
Meanwhile, both sides say they are willing to continue face-to-face negotiations while the court battle unfolds.