Jersey City Mayor Steven Fulop announced Tuesday his city is joining a federal lawsuit challenging a de Blasio administration program that pays for working-class homeless New Yorkers to move across the Hudson River.

Fulop made the announcement as New York City Mayor Bill de Blasio laid out a new $100 million a year effort to tackle the street homelessness in the five boroughs — one of the most visible symptoms of New York’s housing shortage.

“Meanwhile… we’re joining onto the lawsuit from Newark against NYC for pushing their homeless population to NJ cities (including JC without communicating anything or providing proper support,” Fulop wrote on Twitter, linking back to a live feed of de Blasio’s announcement. “That @NYCMayor plan is not solving the problem that is abdicating the responsibility.”

He added: “We are all for working together on solutions in a transparent and open way that works for everyone but up till now the NYC program has been anything but that.”

The Special One Time Assistance program provides families with a steady income who live in city shelters with a year’s rent and other help relocating to cheaper places to live — including outside of the five boroughs.

Since the Department of Homeless Services quietly launched the initiative in 2017, 1,198 families have moved to Newark and 176 families relocated to Jersey City.

De Blasio largely ducked a question about Fulop’s decision at his Tuesday press conference in a church alongside Washington Square Park.

“I haven’t talked to him,” Hizzoner told reporters. “Respectfully, I believe you are relating what you believe to be true but I know Mayor Fulop enough to know if he hasn’t been briefed on this plan he wouldn’t assume the details of it.”

He added: “We’re going to work with all of our fellow mayors, county execs, anyone who wants to try and find a solution to the homelessness crisis, it’s a regional problem, need a regional solution — and, of course, we’re going to defend what we believe are constitutional rights in court.”

It was a shift in tone from his fierce denunciation of the lawsuit during a December 5 press conference, during which he called Newark’s tort “a derogatory lawsuit.”

“It was a statement against working poor people. You read what they’re suggesting,” Hizzoner said. “It’s entirely disrespectful to these people who are just trying to make ends meet and lead their lives.”