A group of far-left activists has claimed it was behind an arson attack on a high-voltage electricity pylon Tuesday that cut off the power supply to Tesla’s factory in Germany.

The activists, calling themselves the “Volcano Group,” claimed responsibility for the fire in a letter published on the alternative German media website Kontrapolis. Police in the German state of Brandenburg told CNN they were aware of the letter and were checking its authenticity.

The group wrote that it had “sabotaged” Tesla (TSLA) because its plant near the German capital Berlin “consumes Earth, resources, people, labor and spits out 6,000 SUVs, killer cars and monster trucks per week.”

“The factory contaminates the groundwater and consumes huge amounts of the already scarce drinking water resource for its products,” the activists said in the letter.

German public broadcaster ZDF reported that the factory had been evacuated and its workers sent home, adding that it was unclear when production would restart. Tesla has not responded to a CNN request for comment.

Commenting on the letter, Tesla CEO Elon Musk wrote on X: “These are either the dumbest eco-terrorists on Earth or they’re puppets of those who don’t have good environmental goals.

“Stopping production of electric vehicles, rather than fossil fuel vehicles, ist extrem dumm.”

Production at the factory is not expected to resume before next week, Reuters quoted plant manager Andre Thierig as saying.

Shares in the maker of electric cars took a beating Tuesday, falling 4.6% in late morning trade in New York.

The attack on the transmission tower also cut off power supply to villages near the factory.

“Thousands of people have been cut off from their basic supply and put in danger. The rule of law will react to such an act of sabotage with the utmost severity,” Michael Stuebgen, the interior minister for Brandenburg, said in a statement, adding that a criminal investigation had begun.

“If the initial findings are confirmed, this is a perfidious attack on our electricity infrastructure. This will have consequences,” he said.

Tesla’s huge plant — located about 30 kilometers (18 miles) southeast of the German capital — is its only one in Europe and is currently capable of producing 375,000 electric cars a year.

Last year, the company lodged an application to ramp up the factory’s production capacity to 1 million electric vehicles a year, which would make it Europe’s biggest car plant.

But in February, local residents voted against a motion to clear enough forest for Tesla to expand the site, leaving it to local authorities to decide how to proceed, according to Reuters.

Since Thursday, around 80-100 environmental activists have been occupying part of the forest near the plant, which Tesla wants to clear for the expansion, ZDF reported Tuesday.

Robin Wood, one of the environmental groups taking part in the occupation of the forest, said it had no information about the reasons for the power outage. “We firmly reject any connection with Robin Wood’s activities,” it added in a statement.

In another setback earlier this year, Tesla said it would pause most production at the Berlin plant for two weeks because attacks on container ships in the Red Sea had delayed the delivery of components. Production was due to resume on February 12, according to CNN affiliate RTL.