• Starbucks fired Alexis Rizzo, the employee responsible for igniting the Starbucks Workers United union campaign, CNBC confirmed.
• Rizzo worked as a shift supervisor at Starbucks for 7 years and served as a leader at the Genesee St. store in Buffalo, New York, which was one of the first two stores in the country to win its union campaign.
• Starbucks Workers United announced Rizzo's termination in a tweet Saturday and said in a corresponding GoFundMe page that "this is retaliation at its worst."

Starbucks fired Alexis Rizzo, the employee responsible for igniting the Starbucks Workers United union campaign, just days after the company's former CEO Howard Schultz testified on Capitol Hill about the coffee chain's alleged union-busting.

Rizzo worked as a shift supervisor at Starbucks for seven years and served as a union leader at the Genesee St. store in Buffalo, New York, which was one of the first two stores in the country to win its union campaign.

Starbucks Workers United announced Rizzo's termination in a tweet Saturday and said in a corresponding GoFundMe page that "this is retaliation at its worst."

"I'm absolutely heartbroken. It wasn't just a job for me. It was like my family," Rizzo told CNBC in an interview. "It was like losing everything. I've been there since I was 17 years old. It's like my entire support system, and I think that they knew that."

Rizzo said her store managers fired her after she finished working her shift Friday. She said they told her it was because she had been late on four occasions — two of which were instances where she had been one minute late.

Starbucks told CNBC Rizzo had missed more than four hours of work over the course of those instances, and that she had been repeatedly issued write-ups for being late. 

Starbucks spokesperson Rachel Wall said separations at the company only follow clear violations of policies. In this case, she said there were numerous attendance violations that were impacting other baristas at this store location.

"We appreciate that our Genesee St. partners provided the Starbucks Experience to each other and our customers this morning, and that area stores continue to serve customers without interruption this weekend," she told CNBC in a statement.

Rizzo said suspects she was let go as a result of Wednesday's Senate hearing.

Schultz faced a volley of tough questions from Sen. Bernie Sanders Wednesday about Starbucks' labor and union practices. Sanders, a pro-union independent representing Vermont, has been putting pressure on Starbucks for more than a year to recognize the union and negotiate contracts with unionized cafes.

Sanders chairs the Senate's Health, Education, Labor and Pensions Committee, which conducted the panel.

During the hearing, Sanders said that Starbucks has engaged in the "most aggressive and illegal union-busting campaign in the modern history of our country." He also accused the company of stalling on collective bargaining agreements, betting that workers will give up and leave the coffee chain.

Schultz defended Starbucks' approach to its negotiations, maintaining that a direct relationship with workers is what is best for the company. He also denied multiple times that the company ever broke federal labor law and said his focus during his time as interim CEO was 99% on operations, not battling the union.

"I don't think it's a coincidence that two days after Howard Schultz had his ego bruised the way that he did that he started lashing out at Buffalo," Rizzo said. She added that two other employees were also fired Friday.

Nearly 300 Starbucks cafes have voted to unionize under Starbucks Workers United, according to data from the National Labor Relations Board. In total, the union has made more than 500 complaints of unfair labor practices related to Starbucks with the federal labor board. Starbucks has filed roughly 100 of its own complaints against the union. Judges have found that the company has broken federal labor law 130 times.

None of the unionized stores have agreed on a contract yet with Starbucks.

Rizzo said she is still "in shock" about being fired, but that she plans to fight for her position.

"We're going to keep fighting to make things right," she said. "I'm going to fight for my job back and to get reinstated."

— CNBC's Amelia Lucas contributed to this report.