A key state lawmaker who championed the union-friendly law requiring New York City to lower class sizes in public schools said he’s open to relaxing the mandate to provide budget relief to Mayor Zohran Mamdani.

“Mayor Mamdani has committed to complying with state law and reducing overcrowding in NYC public school classrooms even though the inaction of the previous administration has exacerbated the difficulty of doing so,” said state Sen. John Liu (D-Queens), who chairs the panel that oversees city education.

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“It’s therefore incumbent upon us to work with him by providing more time and money once he clearly articulates actions to meet those words,” Liu, a former city comptroller, added in a statement to The Post.

Under the state’s 2022 law, 80% of classrooms must have no more than 20 to 25 students by next year, depending on grade level.

All classrooms must abide by those caps by the following 2027-28 school year — 20 students for K-3rd grade, 23 for grades 4 to 8 and 25 for high schools.

Mamdani’s $127 billion preliminary budget plan includes nearly $543 million in additional city spending for the next school year to reduce class sizes.

That estimate nearly doubles, to $943 million annually, in the following three years.

Mamdani voted for the law — a top priority of the powerful teachers’ union — as a state assemblyman.

Facing a multi-billion dollar budget shortfall, the mayor has not publicly asked Gov. Kathy Hochul and the legislature to delay or relax class size deadlines.

But Schools Chancellor Kamar Samuels, in recent testimony, questioned whether schools would be able to hire the thousands of teachers needed to comply with the law, saying reaching the target of 80% of classes by September is a “formidable undertaking.”

Mamdani’s predecessor, Eric Adams, complained the law was an unfunded mandate imposed on the city by Albany.

Chalkbeat first reported Liu’s openness to tweaking the law, though any changes could face resistance from the United Federation of Teachers.

“The law requires capital construction to reduce overcrowded classrooms across the city. At this moment, there is no plan or timeline to do that,” said United Federation of Teachers president Michael Mulgrew.

“Only when a real plan and a clear timeline are in place – not the usual School Construction smoke and mirrors – would we have the information necessary to consider whether any amendments are needed,” added Mulgrew.