Starbucks did not engage in any anti-union practices during its contract negotiations with union employees at its U.S. stores, a report based on a third-party inquiry showed Wednesday.

The coffee chain appointed labor relations expert Thomas Mackall in March on a request by shareholders to look into its labor practices following complaints to the National Labor Relations Board (NLRB) by some employees and labor groups.

They had accused Starbucks of engaging in "union-busting" activities when workers sought better wages, staffing and schedules.

The inquiry conducted from July to September called on Starbucks to improve the way it engages with unionization and revise its Global Human Rights Statement, but said there were no sign that it interfered with the freedom of employees to unionize.

"The assessment was direct and clear that while Starbucks has had no intention to deviate from the principles of freedom of association and the right to collective bargaining, there are things the company can, and should, do to improve its stated commitments," said Mellody Hobson, independent chair of Starbucks.

The NLRB and the union did not immediately respond to Reuters requests for comment.

Starbucks last week reached out to the union representing more than 9,000 of its employees at about 360 of its U.S. stores, where the company proposed to resume with a set of representative stores in January.