Billionaire Elon Musk issued an ultimatum to federal employees Saturday, saying in a post on his social media platform X that employees must respond to an email justifying the work they completed this week or resign.

Federal employees have already begun receiving an email asking to summarize their work, sources familiar with the matter told NBC News, though unlike Musk’s post, it does not explicitly threaten a forced resignation.

The email, sent from the Office of Personnel Management and…