Four US senators have asked Starbucks to disclose how much the coffee chain has spent on lawyers and consulting fees to counter the growing union membership efforts at hundreds of its locations in the US. Senators Elizabeth Warren, Ed Markey and Richard Blumenthal, all Democrats, and independent Bernie Sanders, who caucuses with Democrats, sent their request in a letter late on Tuesday to Starbucks’ chief executive, Howard Schultz, and the company’s board of directors. According to a copy of the letter seen by Reuters, the senators cited “reports that Starbucks is engaging in illegal union-busting tactics” and asked Starbucks to respond within a month. “We appreciate every opportunity to share the facts and address inaccuracies about our company and our partners, and we are confident in our stringent compliance with federal labor law,” Starbucks said in response to receipt of the letter. Employees at about 245 of Starbucks’ nearly 9,000 company-owned US locations have voted to unionize in just over the past year. The senators also said in their letter that they want to see the guidance Starbucks gave to managers about how to deal with workers organizing unions and whether its spending expenditures to counter unions were listed in its tax filings. They also asked for a list of changes the Seattle-based chain has made to benefits for non-unionized employees. The company has been boosting benefits – including expanded coverage for child adoption services – but only for employees not belonging to a union. Starbucks is “weaponizing benefits and wage increases to discourage workers from organizing”, Warren said in emailed remarks to Reuters. Bargaining is tentatively set to begin on various days this month at some stores. In August, the National Labor Relations Board accused Starbucks of illegally withholding raises from unionized workers. Starbucks said on a company blog that labor law requires it to negotiate any changes in benefits or working conditions with the union representing those employees.