A group of four restaurant owners in Boston's North End neighborhood has filed a lawsuit against Boston Mayor Michelle Wu, claiming the $7,500 outdoor dining fee imposed only on North End restaurants was unconstitutional.The lawsuit was filed Monday in the U.S. District Court for the District of Massachusetts, eight days after North End restaurants were first allowed to start offering outdoor dining this year.The plaintiffs listed on the lawsuit are Jorge Mendoza, owner of Vinoteca di Monica; Carla Gomes, owner of Terramia Ristorante and Antico Forno; Christian Silvestri, owner of Rabia's Dolce Fumo; and Patrick Mendoza, owner of Monica's Trattoria."It's a principle thing. You're not going to isolate the North End and we're not going to back down. We're going to fight for what's right," Silvestri told NewsCenter 5's John Atwater.The lawsuit also mentions that the plaintiffs took issue with the policy that every parking space a restaurant took up in order to place tables on would cost an additional $480 per month. The plaintiffs believe that no restaurants in Boston, except for those in the North End, must pay for the use of parking spaces in the outdoor dining program.Wu said the $7,500 fee was imposed only on North End restaurants because of the neighborhood's unique challenges with outdoor dining, including traffic and pedestrian access, parking and trash pickup."That's 625 plates of pasta I need to sell to break even. That's a lot of pasta," Silvestri said. "We wash our sidewalks ourselves. We have an outside independent contractor take our garbage. I mean, there are rats everywhere in Boston."Jorge Mendoza has been one of the most vocal opponents of the $7,500 outdoor dining fee, a fee that was not imposed on restaurants in other Boston neighborhoods. He was among the North End restaurant owners who threatened to sue Wu and the city in March. In turn, Wu sent a letter to North End restaurant owners to signal that City Hall would be prepared to rescind outdoor dining in that neighborhood if a majority of restaurant owners believed the proposed program for the upcoming season is "unworkable."In addition, Jorge Mendoza accused Wu of intentionally shutting North End restaurant owners out of a March 29 news conference when it was moved to a smaller room that accommodated fewer people.Wu held firm on the $7,500 fee but said North End restaurants could apply for a hardship waiver that could drop the fee to $5,000 or $3,000 and offered the option to pay the fee in monthly installments.On May 1, city officials said they received 67 outdoor dining applications this year compared to the 77 outdoor dining areas that were approved at North End restaurants last year. In addition, the city received 28 hardship waiver applications from North End restaurants, 23 of which were granted.Jorge Mendoza said he is offering outdoor patio seating at his restaurant because it would be difficult to compete with other North End restaurants if he did not offer outdoor dining.Mendoza, however, said on April 27 that he was planning on suing the city for damages after spending approximately $20,000 to offer outdoor dining this year."It's a complete injustice, alright. It's completely mismanaged," Mendoza said. "This could've been done in a completely different way that it would not affect the city, the neighbors and the businesses adversely." The lawsuit stated that several of the plaintiffs have enrolled in the city's payment plan to pay the $7,500 outdoor dining fee in order to stay competitive."If you have one guy who's going to do it next door, he's going to get all the people to go outside. So you're almost forced to do it and then fight later, which is what we're doing," Silvestri said.According to the lawsuit, the plaintiffs believe Wu violated their rights to due process of law and equal protection and equal treatment, which are guaranteed by the U.S. Constitution. The lawsuit also claims the mayor's actions violated the Commerce Clause of the U.S. Constitution and set up "unfair methods of competition" and/or are "unfair or deceptive practices" in "commerce." A city spokesperson said Wu's office is declining to comment on the lawsuit. The 2022 outdoor dining season in the North End is scheduled to run through Sept. 5, but Wu's office previously said that date may be pushed back to Sept. 30 pending compliance.The outdoor dining season for all other Boston neighborhoods started April 1.