Mayor Bill de Blasio and Sens. Chuck Schumer and Kirsten Gillibrand rallied alongside local union workers in Manhattan on Sunday, vowing to wage a grass roots fight to defeat the GOP’s proposed tax overhaul.

“The grass roots is where the decision ultimately gets made and the people are going to fight this,” de Blasio told dozens of members of the United Federation of Teachers, 32BJ-SEIU, and New York State Nurses Association who crowded into the lobby of New York city hall.

“We were able to defeat Trumpcare three times . . . we must do the same to defeat this tax plan,” said Gillibrand (D-N.Y.), referring to the failed attempts by Republican leaders to repeal and replace the Affordable Care Plan earlier this year with a plan back by President Donald Trump. Congressional Republicans failed to garner enough support for a replacement measure amid a wave of protests at town hall meetings across the country.

Schumer (D-N.Y.), the Senate Minority leader, took aim at six House Republicans from upstate, and six Republican members of Congress from New Jersey who have supported the House tax plan. He told the crowd they “have to choose their states over the rich special interests who are trying to push them around.”

“This is not a partisan issue,” Schumer said, before giving a “shout out” to Reps. Pete King (R-Seaford), Dan Donovan (R-Staten Island) and Lee Zeldin (R-Shirley) for speaking out publicly against the plan. The lawmakers have said they oppose the plan, in part because it would eliminate state and local property taxes from the list of tax deductions that can be claimed by taxpayers to reduce their federal income tax burden.

Schumer and King have said eliminating the so-called SALT deductibility would amount to “double taxation” and primarily hurt taxpayers in states with higher property taxes such as New York, New Jersey and California.

The House GOP tax plan would eliminate other popular tax deductions such as interest paid on student loan debt and deductions for medical expenses that exceed 10 percent of a taxpayer’s income, according to the measure introduced last week. Democrats argue that eliminating the deductions amounts to a tax hike on middle-class Americans. Republican leaders, including Treasury Secretary Steven Mnuchin, have dismissed the claim, arguing in part that deductions such as the property tax write-offs would not be missed if state governments such as those in New York and New Jersey cut their budgets and trimmed their spending.

De Blasio, citing figures compiled by his office, said 700,000 city taxpayers would see some level of tax increase under the plan.

Reps. Nydia Velazquez, Joseph Crowley (D-Queens), Gregory Meeks (D-Queens), Jerry Nadler (D-Manhattan), Carolyn Maloney (D-Manhattan), Hakeem Jeffries (D-Brooklyn) and Yvette Clarke (D-Brooklyn) also spoke at the rally, all casting the proposal as an “assault” on the middle class.

“This bill takes a wrecking ball to our middle class,” said Velazquez, who represents portions of Brooklyn and lower Manhattan.

A state GOP spokeswoman could not immediately be reached for comment Sunday.