BOSTON – Boston Mayor Marty Walsh endorsed Hillary Clinton at a charged rally in historic Faneuil Hall Sunday afternoon with hundreds of union members as Clinton rolled out a $275 billion infrastructure plan.

“Get your sledgehammers ready, we’ve got a glass ceiling to demolish!” Walsh declared to cheers as they launched an initiative dubbed “Hard hats for Hillary.”

“Nobody comes closer to her experience, nobody comes closer to her achievements,” Walsh continued, adding that he chose Clinton because she was “battle-tested” and “gets the job done.”

Walsh is an up-and-coming Democrat elected two years ago to replace Tom Menino, Boston’s longest serving mayor – and his endorsement carries more weight than most. In a Democratic bastion like Boston, the mayor heads a powerful political machine that will help Clinton in Massachusetts’ primary on March 1. His party’s apparatus can also send support to her in New Hampshire’s first-in-the-nation primary, and draw attention to Clinton in Boston’s media market, which reaches across the border.

Walsh, a former union member himself, told reporters before the event that he hesitated a bit on the endorsement as he waited to see whether Vice President Joe Biden would get in the race. But he added that he would do anything the Clinton campaign asked, saying his endorsement was not in name only.

By the time Clinton took the stage, the 800 supporters packed inside the room had been worked into a fever pitch with impassioned speeches by union presidents and praise for the New England Patriots.

“I can’t tell you how pleased and proud I am to have the endorsement of your fabulous mayor Marty Walsh,” Clinton said.

Orange-t-shirt clad LIUNA members turned out in force and dotted the audience in hardhats. The Carpenters union made special shirts for the occasion, showing both their and Clinton’s campaign logo.

Terry O’Sullivan, the president of the Laborers International Union (LiUNA), which also recently endorsed Clinton, said the former secretary of state “understands unions,” adding that organized labor will make this election.

After portions of usual stump, Clinton teased a proposal to spend an additional $275 billion on infrastructure projects over five years, on top of money she said Congress should already authorize.

A campaign aide added that the bulk of that – $250 billion – would go to direct investment by the federal government, while the remaining $25 billion would support a national Strategic Infrastructure Bank, which would fund future projects through a combination of financing mechanisms.

The aide said the plan would be paid for by business tax reform, but did not offer more details of the pay-for.

Infrastructure spending has been a top priority of President Obama’s as well, but his plans have so far failed to go anywhere in the Republican-controlled Congress. Clinton’s proposal would face the same opposition in Congress, which is likely to have at least one chamber under GOP control if she wins the presidency.

Clinton also took a veiled shot at Democratic rival Bernie Sanders, without mentioning him by name. Clinton has sparred with Sanders in recent weeks over his single-payer health plan, which would be paid for by tax increases on all Americans. Clinton has vowed not to raise taxes on those who make $250,000 or less per years.

“I’m the only Democrat in this race pledged to raise your income, not your taxes,” she said.