California sued the Trump administration on Monday over its decision to send in National Guard troops in response to protests over immigration enforcement, calling it an unconstitutional use of executive power that usurped the state’s authority.

U.S. officials said about 1,000 National Guard members were in the city under federal orders by midday Monday.

The order would put them on active duty. One official warned, however, that the order was just signed and it could take a day or two to get troops moving.