Billionaire Elon Musk, who is leading Trump’s Department of Government Efficiency scouring government agencies for suspected waste, delivered a warning Monday to workers on his platform X. “Starting this week, those who still fail to return to office will be placed on administrative leave,” Musk wrote.

Elon Musk caused alarm among federal employees and drew ire over an email sent on Saturday requesting that employees summarize their work for the week, and warning on social media that a failure to do so would be taken as a resignation.

Attorneys representing unions, businesses, veterans and conservation organizations filed an updated lawsuit in federal court in California on Monday, arguing Elon Musk had violated the law by threatening mass firings.