Vermont Sen. Bernie Sanders is raising the stakes in his effort to get Starbucks’ interim CEO Howard Schultz to testify at a Senate hearing about an ongoing unionization effort at the company.

Sanders, chairman of the Senate Health, Education, Labor and Pensions Committee, said Wednesday that the committee will vote March 8 on whether to issue a subpoena to Schultz.

If the vote passes — and it’s likely it would, since Democrats are in the majority on the committee — Schultz would be required to appear before the committee on March 15.

In a statement, Starbucks called Sanders’ announcement a “disappointing development” and reiterated its offer to send AJ Jones II, its chief public affairs officer, to testify instead. Starbucks said Jones has been more closely involved with the unionization effort.

At least 289 company-owned U.S. Starbucks stores have voted to unionize since late 2021. Union supporters say they want higher pay and more consistent schedules, among other issues.

Seattle-based Starbucks doesn’t support unionization, saying it already provides industry-leading benefits and can run the company more effectively when it works directly with employees.

The process has been contentious. Regional officers for the National Labor Relations Board have filed 79 complaints against the company for various issues, including failure to bargain, according to a board spokesperson.

Starbucks, meanwhile, has filed 102 unfair labor practice charges against the union, Starbucks Workers United.

In a statement, Sanders said he was taking the rare step of voting to subpoena because Schultz hasn’t responded to repeated requests to meet and provide documents to the committee. Sanders wants to question Schultz about reports that it has fired more than a dozen pro-union workers, among other things.

“While Howard Schultz is a multi-billionaire who runs a very profitable multi-national corporation he must understand that he and his company are not above the law,” Sanders said.

Schultz has previously refused to appear before the committee. In a letter sent to the committee in mid-February, Starbucks noted that Schultz — a longtime Starbucks leader who came out of retirement last year to assume the interim CEO job — will be transitioning out of that role at the end of this month. Laxman Narasimhan, a former PepsiCo executive, will become Starbucks’ new CEO on April 1, but Schultz will remain on the company’s board.