The city’s firefighters union is suing City Council Speaker Melissa Mark-Viverito over a controversial vote regarding disability pensions.

The Uniformed Firefighters Association wants newly-hired members to receive the same disability benefits as those hired before changes were made to the pension system in 2009.

The de Blasio administration also wants changes, but more modest ones than the union proposal.

The Council voted last month to approve the Mayor’s plan.

The suit, filed Monday by the union, claims Mark-Viverito acted improperly and obstructed debate, leading to a last-second vote on the mayor’s plan and no vote or discussion of a competing proposal.

The speaker’s office is declining to comment until more details on the suit are released.

Union President Steve Cassidy will be a guest Tuesday on "Inside City Hall" at 7 and 10 p.m.