Mayor Mitch Landrieu may have some quiet weekends at home ahead of him — by court order.

A decades-old legal fight over $75 million worth of back pay — plus $67 million in interest — the city owes to firefighters took a dramatic turn on Friday as Civil District Court Judge Kern Reese finally made good on a threat to hold City Hall in contempt for refusing to pay up.

Reese said he would place the mayor under house arrest on weekends if the case isn’t resolved in a week.

“I understand the budget of the city,” Reese said, addressing Landrieu and five members of the City Council who joined him in court Friday.

“I understand the travails that the administration goes through to try to provide services for the citizens of the city. But this is a legal issue, and everyone has to have deference and respect for the law. It has to be done, and we’ve waited long enough.”

Shortly afterward, Landrieu canceled an appointment he had to “swim with the sharks” at the Audubon Aquarium of the Americas and held a news conference to say that City Hall cannot afford to pay a judgment that, even spread over several years, could eat up a large share of the city’s roughly $540 million annual general-fund budget.

“I am prepared to stay under house arrest for the next two years of my term, because this is too important for the city,” Landrieu said.

He joked that this his wife, Cheryl, has been asking him to take weekends off for 25 years and has a long “honey-do” list ready for him.

He called Reese’s ruling “unprecedented” and denounced the firefighters for a “scorched earth policy and strategy that threatens to severely cripple this city’s ability to deliver essential services.”

Nick Felton, president of the firefighters union, called Landrieu’s reaction to the order a “thug statement.”

“That’s pretty ludicrous for any elected official to say he’s going to continue to violate the law,” Felton said. “He’s come to his day of reckoning. He’s not going to bully his way through the court system and bully the firefighters.”

The threat from Reese was the first time that he has spelled out what it would mean if the mayor were held in contempt for refusing to pay the firefighters. He said Landrieu would have to remain in his home from 5 p.m. on Friday to 5 p.m. on Sunday. The mayor would need specific permission from the court to leave in emergency situations.

City attorneys have already begun appeals to both the 4th Circuit Court of Appeal and the state Supreme Court seeking to invalidate the order.

The threat of house arrest would appear to give the firefighters added leverage as negotiations with the Mayor’s Office continue. But it’s unclear whether it will accomplish Reese’s goal of finally resolving a lawsuit that dates back to the 1970s.

“The judge put (Landrieu) at risk, hoping that would result in both parties going back to the bargaining table,” said Chick Foret, a local lawyer.

But he pointed out that Reese’s move puts pressure on only one side of the dispute, leaving the firefighters free to continue balking at the city’s proposals unless they get 100 percent of what they want.

The city’s latest proposal called for paying out $75 million over 30 years, compared with a previous offer of $45 million over 13 years.

The full judgment amounts to $75 million plus $67 million worth of interest for state-mandated pay raises that the city failed for many years to implement, claiming they were illegal and unjustified. The courts have consistently sided with the firefighters.

Felton has said the city should be given no more than six to 10 years to pay.

Complicating the talks is a separate lawsuit in which the firefighters pension system sued Landrieu for failing to pay the full amount of the city’s required contributions early in his term. That suit also involves tens of millions of dollars.

The Landrieu administration has said that both cases must be resolved at the same time, and that any solution must involve firefighters accepting less generous pension benefits.

Reese said he has no jurisdiction over the pension case, which is overseen by Civil District Court Judge Robin Giarrusso, but he did concur with the mayor in suggesting that firefighters might need to bend on pension issues to put the fund on a solid footing. “Everyone needs to be responsible,” he said.

Reese has not spelled out exactly what he thinks City Hall should pay or how quickly. He said he does not expect the city to come up with the full judgment immediately, but he said it would be “absurd” for the last installment to come 50 years from now, which was possible under one of the scenarios floated this week.

Landrieu’s appeal of the contempt order is likely to center on the argument that Reese is usurping one of the mayor’s and City Council’s most basic functions: deciding how to spend tax dollars.

In his news conference, the mayor said Reese’s order “undermines the very fundamental principles of our Constitution and disrupts the separation of powers.”

Foret said the main questions for appeals courts will be whether Reese has the authority to keep Landrieu in his home, and whether the mayor is really the appropriate official to target, given that the council has the final say on budget decisions.

Aside from the appeal, he said, Landrieu could end up turning the tables by offering the firefighters a deal that Reese finds reasonable.

“I wouldn’t be a bit surprised if the mayor does everything he can to make a good-faith effort to resolve this, and then the judge turns his chair over to the firefighters and says, ‘OK, now it’s your turn,’ ” Foret said.