Federal agencies swiftly sued the American Federation of Government Employees last week, asking a lone Trump-appointed judge to uphold an order banning unions for two-thirds of the federal workforce.

Donald Trump’s administration moved to invalidate contracts between a swath of US government agencies and the largest federal union representing their employees, marking a sweeping attack on collective bargaining rights as the president aims to lay off government workers.

Trump, citing the Civil Service Reform Act of 1978, says he has the authority to make the move owing to national security concerns. The American Federation of Government Employees, however, disagrees and says the matter will quickly end up in court.