Some 100 workers at Tesla’s Gigafactory walked out in protest recently after learning that a contractor on the site is using workers from outside the state. Tesla’s 10-million-square-foot facility situated outside Reno, Nevada broke ground in June 2014 and has been ahead of its construction schedule. It’s uncertain how this walkout will impact work on the site.

Union workers are upset that laborers from Arizona and New Mexico are being brought in by Brycon Corp, a nonunion contractor. Following the walkout, Tesla issued an e-mail statement in response, which Bloomberg cites as defending the contractor, without identifying the company by name, as using more than 50 percent Nevada workers. Tesla noted that more than 75 percent of the factory workforce is comprised of residents of that state. Company officials haven’t commented on the potential fallout of the union walkout.

Related: Take a first look at the gigantic Gigafactory Tesla is building in Nevada

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The Gigafactory is a $5 billion plant Tesla is constructing to house production for its batteries, and will be powered completely by renewable energy. Early quips suggested the factory would be the biggest building on Earth. If Tesla holds to its plan to eventually expand to 24 million square feet, then it will certainly be true.

Workers who participated in the walkout are part of the Building and Construction Trades Council of Northern Nevada, a labor union first established in 1928. Union president Todd Koch said it was a “slap in the face” to Nevada workers to see out-of-state license plates in the factory’s parking lot. In Tesla’s written statement, the company said the walkout doesn’t represent any complaints about its treatment of workers, but stems solely from the issue of workers employed by third-party contractors.

Via Bloomberg

Images via Tesla Motors