House Republicans issued a subpoena for documents to the National Labor Relations Board on Wednesday, alleging misconduct by its officials in union elections involving Starbucks Corp.

In a letter to the federal labor agency, Rep. Virginia Foxx, R-N.C., the chair of the Education and Workforce Committee, cited a letter Starbucks wrote to NLRB officials in August, alleging that they "engaged in substantial misconduct” in connection with an election involving the company and Workers United at a Kansas store.

Foxx said she believes an NLRB report last month “confirmed certain allegations” detailed in the letter from Starbucks.

The report shows NLRB officials “shared substantially more information” about the election with Workers United than with Starbucks, Fox wrote, adding that the hearing officer “found the disparity so great that it 'casts doubts as to the fairness of the conduct of this election.'"

The news was first reported by The Wall Street Journal.

Foxx asked that the NLRB provide communication and documents related to the matter to the committee on March 29, her office confirmed.

That is the day Howard Schultz, who recently stepped down as Starbucks' interim CEO, is set to testify before the Senate Committee on Health, Education, Labor and Pensions, chaired by Bernie Sanders, I-Vt.

Sanders, who is pro-labor, is investigating dozens of allegations that Starbucks breached federal labor law, as well as other complaints against the company under Schultz' leadership.

The company has fought back, defending itself from the allegations and filing countercomplaints against the unions.

The NLRB, Starbucks Corp. and Starbucks Workers United did not immediately respond to requests for comment.

More than 250 of Starbucks’ thousands of company-run stores in the U.S. have voted to unionize since late 2021; the company has opposed the efforts.

As part of a lengthy unionization campaign, Starbucks' workers across 100 stores planned a three-day strike in December.

This article was originally published on NBCNews.com