Starbucks is under fire over the company’s response to unionization efforts as senator Bernie Sanders threatens to call its chief executive before his committee on alleged labor violations and staff petition for it to end “intimidation” of organizers.

Sanders, chairman of the Senate health, education, labor and pensions (Help) committee, announced on Wednesday that the committee will be voting on whether to issue a subpoena to compel the Starbucks chief, Howard Schultz, to testify about Starbuck’s federal labor law violations, and to authorize a committee investigation into labor-law violations committed by major corporations.

“For nearly a year, I and many of my colleagues in the Senate have repeatedly asked Mr Schultz to respect the constitutional right of workers at Starbucks to form a union and to stop violating federal labor laws,” Sanders said in a press release confirming the 8 March vote.

“Mr Schultz has failed to respond to those requests. He has denied meeting and document requests, skirted congressional oversight attempts, and refused to answer any of the serious questions we have asked. Unfortunately, Mr Schultz has given us no choice but to subpoena him.”

The move came after 44 employees at Starbucks headquarters in Seattle and 22 additional anonymous employees signed on to a petition calling on the company to reverse a return-to-office mandate and “to commit to a policy of neutrality and respect federal labor laws by agreeing to follow fair election principles, and allow store partners, whether pro- or anti-union, to decide for themselves, free from fear, coercion, and intimidation”.

According to Starbucks Workers United, more than 200 Starbucks workers have been fired in retaliation for organizing. The National Labor Relations Board has alleged that Starbucks has fired over 60 union leaders across the country. Starbucks has aggressively opposed unionization efforts from the first stores to unionize in late 2021 in Buffalo, New York, to over 350 stores around the US that have held union elections. More than 280 stores have won union elections, though a first union contract has not been reached at any store so far.

On Tuesday, administrative law judge Michael A Rosas issued a sweeping decision in Buffalo, ordering the reinstatement of seven fired Starbucks workers with back pay, and issuing a bargaining order for three Starbucks stores. The order requires 27 workers to be reimbursed for lost wages, for Schultz and the senior vice-president of operations, Denise Nelson, to read a notice or make a video for employees in Buffalo informing them of their rights, and for the company to post a national physical and electronic notice.

“It’s what we, the workers, have been saying for more than a year now: that Starbucks, at every chance they get, bust the union and get us to be intimidated by it,” said Austin Locke, an employee for nearly six years in New York who was fired and recently won reinstatement after the city sued Starbucks under “just-cause” protections. “They’ve just been stonewalling us the whole time.”

“The news of this win is single-handedly the most exciting thing that’s happened in this campaign thus far,” said Michael Sanabria, a barista from the Transit Commons location in Buffalo, New York, in a press release on the decision.

“Having to reinstate all of these workers, reopen the first Starbucks location closed in the name of union-busting, and most importantly, post notices in every single store across the country for the duration of the Starbucks organizing campaign is such a massive win for us, and for the labor movement as a whole.

“After waiting through months of Starbucks’ stalling tactics, this will reinvigorate and re-energize the momentum of this movement.”

The Guardian has contacted Starbucks for comment.