A bill to boost New York City teaching assistants’ pay by $10,000 has become law despite Mayor Zohran Mamdani opting not to sign it — and it could still be challenged in court.

The law giving raises to paraprofessionals went into effect Wednesday after Mamdani did not take official action, the United Federation of Teachers union, announced.

The powerful teachers’ union had backed the “Respect for Paraprofessionals” bill, which the City Council passed unanimously last month.

“Our paraprofessionals made this happen,” UFT President Mike Mulgrew said. “We thank Council Speaker Julie Menin, Labor Chair Carmen De La Rosa and the Council members who fought so hard to get this law passed and address a long-standing injustice.”

But Mulgrew cautioned that Mamdani could decide to challenge the legislation in court, claiming it violates labor law governing collective bargaining.

“We are prepared for this. The bill was drafted carefully to ensure that it does not violate the state Taylor Law, which governs collective bargaining,” Mulgrew said.

“We hope it won’t come to this, but if it does, we are prepared to engage in a legal fight for the RESPECT check and the paraprofessionals who keep our schools running.”

Mamdani, a former state assemblyman, personally backed the pay hike bill during last year’s mayoral campaign, while accepting the UFT endorsement for the general election.

The mayor changed his tune before the council passed the bill, saying that paraprofessional pay was a “matter that is best treated at the bargaining table,” not through legislation.

But he still insisted the law would be upheld.

Government watchdogs slammed the legislation as a dangerous precedent, giving the green lights to other unions to sidestep collective bargaining and appeal to the council to settle pay dispute, driving up costs to the city.

In a note to paraprofessionals — teaching assistants who help students with disabilities — Mulgrew said they can expect the $10,000 bump in four installments of $2,500 each on January 1, 2027, March 1, June 1 and August 1.

Starting pay for paras is $33,000 and reaches $56,000 after 15 years.

“Today, we celebrate accomplishing the goal that we began fighting for almost two years ago. The RESPECT check legislation has become a law that will give our hardworking paraprofessionals more money this coming year,” Mulgrew said.

Mamdani’s office had no immediate comment.