(CNN) — Tesla has fired more than 30 supporters of a nascent union at its Buffalo facility, just days after the organizing effort was announced, according to the union.

The union, Tesla Workers United, has filed a complaint with the National Labor Relations Board alleging the company illegally fired its supporters.

The complaint lists the names of 18 employees it charges were fired "in retaliation for union activity and to discourage union activity." But a statement from the union said that more than 30 employees were fired. It said the firings came on the heels of the union organizing effort announced earlier this week.

"I feel blind sided," said Arian Berek, one of the fired employees quoted in the union's statement. "I got Covid and was out of the office, then I had to take a bereavement leave. I returned to work, was told I was exceeding expectations and then Wednesday came along. I strongly feel this is in retaliation to the committee announcement and it's shameful."

The people fired worked on labeling data collected as part of Tesla's Autopilot technology. Tesla CEO Elon Musk has praised the work of this group, saying that it is the "Holy Grail" of the company's self-driving technology.

"We're getting quite good at auto labeling," he told investors in April 2021. "The trainers train the training system and then the system auto labels the data and then the human laborers just need to look at the labeling to confirm that it is correct and perhaps make edits."

But union supporters object to productivity expectations they describe as "unfair, unattainable, ambiguous and ever changing." They also object to the company allegedly monitoring their keystrokes to measure their work.

"We're angry. This won't slow us down. This won't stop us. They want us to be scared, but I think they just started a stampede. We can do this. But I believe we will do this," said Sara Costantino, a current Tesla employee and organizing committee member, in the union's statement.

The plant in Buffalo does not build cars. In addition to the Autopilot labeling work, it builds solar panels and related products.

The new union is receiving support from the Starbucks Workers United union, which has organized more than 200 Starbucks stores in just over a year, and the Service Employees International Union. Starbucks Workers United's first victory came in Buffalo, and it is particularly strong in Western New York.

In the past, Tesla has been accused of illegally firing union supporters at its plant in California, its first to build cars. But efforts to organize that plant have fallen short of the union's filing to hold votes among employees there.

Musk has repeatedly criticized unions in tweets, one of which the NLRB ordered him to delete three years after it was posted.

Tesla, which has disbanded its public relations staff and has not responded to press inquiries for several years, could not be reached for comment.

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