An executive who played a key role in the company's response to a growing union campaign is leaving by the end of the month.

Rossann Williams, the president of retail for North America, is leaving Starbucks after 17 years. The letter said that the decision was preceded by discussion about a next opportunity for Rossann.

Ms. Williams has been a champion of our mission, our culture and operational excellence, according to the letter.

The Starbucks store in Buffalo became the only Starbucks store in the country with a union.

More than 175 elections in which the National Labor Relations Board has declared a winner have been won by the union.

In the fall, Ms. Williams went to the city to lead the company's response to the campaign. She spent a lot of time in stores asking employees about concerns they had at their workplace.

Some workers said the presence of such a high-ranking official in their stores was frightening.

Ms. Williams and other Starbucks officials could be in violation of labor laws if they try to improve working conditions if employees vote against unionization.

The National Labor Relations Board looked into the accusations and found merit to them.

The company denied that it had broken the law and said that it was trying to address operational issues like understaffing and inadequate training.

Ms. Williams said in an interview in October that she had no choice but to intervene after being asked if she or the company might be trying to undermine the union election.

She said that it would be against her job if she didn't do anything about the condition of the stores. I wouldn't be able to say I'm not going to do anything.

Ms. Williams would be replaced by Sara Trilling, who was most recently in charge of the company's operations in the Asia- Pacific region.