It might seem a tad hypocritical for Mayor Vincent Gray to appeal to Congress to intervene in a local budget matter at the same time he's asking for budget autonomy. But that's where he finds himself.

In the fine print of the 2013 Budget Request Act, Gray has asked Congress to enforce a 2000 law affecting union contracts and overtime pay retroactively. Why would the city ask Congress to reach back 13 years to affirm this obscure language?

Short answer: $36 million.

That's the amount of overtime pay D.C. firefighters claim they are due going back to 2001. The firefighters union and the city have been tussling over the backpay since 2007. The union has prevailed in administrative proceedings and in court. Facing the prospect of forking over $36 million, the mayor wants Congress to intervene and wipe away the bill.

It flies in the face of Home Rule for any mayor to resort to asking Congress for help. Perhaps that's why city council Chairman Phil Mendelson flagged the language when he convened the first budget hearing Monday. The city "could be on the hook for this significant payment," he said.

Mendelson alerted Ed Smith, president of the D.C. Firefighters Association. It took Smith a while to sort it out, but here's the story.

When the city was going broke in the late 1990s and the federal control board took over its finances, the board wiped out all of the collective-bargaining agreements, in part to control overtime. The firemen said the control board had exceeded its power and sued. The control board asked Congress to give it the authority, which it did. But a congressman notified the city that the law would last only one year, unless it was reauthorized. It was not.

When the city regained control of its finances in 2001, the firefighters figured they were working under their existing contract, which paid overtime. In 2007, they presented the city with a $36 million bill for overtime pay. The city invoked the control board law and refused to write a check. The two sides went to war.

The city argued its side before the Public Employee Relations Board. The board in 2011 found "no merit" in the city's various reasons to withhold the backpay. The city appealed to the Superior Court. The judge affirmed the board's ruling against the city.

Time to pay up? Nope. The city has taken its case to the D.C. Court of Appeals.

But the city's lawyers know they face long odds on appeal, so they recommended the nuclear option: asking Congress to reaffirm its law wiping out union contracts back to 2000. Seems like a long shot to me.

"We find it anti-labor and absolutely inappropriate," Smith says.

A city budget official said the law is on their side, and, anyway, it doesn't have the dough. Smith tells me he's tried to negotiate and settle the matter, but the city has never responded.

Unless Congress responds, the union's response will be: Fork it over.

Harry Jaffe's column appears on Wednesday. He can be contacted at hjaffe@washingtonian.com.