Mayor Bill de Blasio is getting slammed by the Transport Workers Union again with a full-page ad in Monday's edition of the Daily News. NY1's Jose Martinez filed the following report.

When Bill de Blasio ran for mayor in 2013, he was endorsed by Transport Workers Union Local 100, which represents more than 30,000 bus and subway employees.

But that seems like a long time ago.

"It's not a question of him doing us wrong. It's a question of him underfunding the MTA capital budget," said John Samuelsen, president of TWU Local 100.

On Monday, the union threw a roundhouse right at the mayor, paying for a full-page ad in the Daily News showing him leaning out of a graffiti-scarred train. It says he risks taking the transit system back to the bad old days of the 1970s and '80s if the city doesn't pump billions more into the state-run MTA.

"Those are the dark days that we must avoid at all costs," Samuelsen said. "Mayor de Blasio must step up, pay his fair share and provide a safe, reliable system for New York's working families."

The mayor fired back at the union's printed potshot.

"I think the ad is pitiful," de Blasio said. "I think it's  misleading, and it doesn't tell people the truth. The truth is, the MTA is the state's responsibility."

The union's attacks appear to be the latest extension of de Blasio's bitter feud with Governor Andrew Cuomo, who oversees the state-run MTA and its chairman and CEO, Thomas Prendergast.

Over the past several weeks, Prendergast has repeatedly accused de Blasio of shortchanging the transit system by not committing billions of additional city dollars to the MTA's five-year Capital Program.

When a G train derailed in Brooklyn, the union bashed de Blasio, too, warning of more accidents unless he comes through with more money.

"All of the dire warnings in that ad should be addressed to the state of New York," de Blasio said.

City Hall has repeatedly said that the state shouldn't be recruiting surrogates to go after the mayor in the fight for transit funding. The union, though, says it didn't need any prompting to join this battle.

"We're looking at a situation where the tracks are falling apart, stations are crumbling and an investment is necessary," Samuelsen said.

One that de Blasio says the city is willing to make, so long as the state takes what he calls "full responsibility."