Starbucks is pushing back against Sen. Bernie Sanders, I-Vt., and the Senate Health, Education, Labor and Pensions Committee he chairs ahead of a vote expected next week to subpoena interim CEO Howard Schultz as part of an investigation into federal labor law.

“Respectfully, Howard Schultz is not the right witness for the hearing,” Zabrina Jenkins, Starbucks’ acting executive vice president and general counsel, wrote in the letter, which was addressed to Sanders, ranking member Bill Cassidy, R-La., and the rest of the HELP Committee.

Jenkins said Schultz “assumed the interim ceo role nine months after the issues regarding unions arose and has been focused on the reinvention plan of Starbucks since that time.” She said he will “cease to be the interim ceo of the company this month.”

Sanders, who built his national profile as a pro-labor populist, is trying to investigate dozens of complaints that Starbucks violated federal labor law and other accusations of unfair labor practices leveled against the company under Schultz’s leadership. Starbucks has defended its actions, including filing countercomplaints against the unions.

Sanders quickly rejected the request, responding in a letter that “the Senate HELP Committee invited Howard Schultz to testify, not a subordinate, because he is the man who engineered and continues to make labor decisions at Starbucks.”

The company asked that others testify instead. Jenkins offered herself, as well as AJ Jones II, the executive vice president and chief communications officer, and May Jensen, the vice president for partner and labor relations.

Sanders told NBC News this week that he expects to hold a committee vote next week on subpoenaing Schultz and that he’s eying March 15 for him to testify.

“Look, the bottom line here is not complicated. You have a multibillionaire named Mr. Schultz, who’s head of a profitable, multinational corporation, who apparently thinks that he doesn’t have to pay attention to the law,” Sanders said, mentioning citations against him by the National Labor Relations Board. “That’s not what should go on in America. We all have should have one system of justice, whether you’re a billionaire or whether you’re anybody else. And unfortunately, we don’t have that right now. So I look forward to having Mr. Schultz before the committee to answer questions why he thinks he can break federal law.”

A subpoena requires majority support on the committee, on which Democrats have an 11-to-10 advantage over Republicans. Cassidy said he won’t support the subpoena.

“I think we’re in pretty good shape,” Sanders said. “I think we’re strong among the Democrats. And I hope that we’ll have Republican support, as well.”