() A federal request for 20,000 National Guard troops to help with immigration enforcement would probably need some kind of sign-off from state governments, a Trump administration advisor said Friday.

The Department of Homeland Security, which oversees Immigration and Customs Enforcement, asked the Pentagon for the National Guard’s assistance for roundups nationwide, and defense officials are reviewing the request, The Associated Press reported.

Governors typically control National Guard units in their respective states, with exceptions, and it’s not clear how the DHS request would be executed or whether all governors would be on board.

“I think states are going to have to be involved in assigning National Guard,” Ron Vitiello, a senior adviser for U.S. Customs and Border Protection, said during an appearance on “The Hill” on Friday.

Vitiello said he hasn’t seen details of the request but noted thousands of active-duty troops are already assisting U.S. Border Patrol along the southern border. He said National Guard members likely would be “more boots on the ground” assisting ICE agents in the interior.

“This is the ICE mission: They’re going after the worst of the worst, in every city and town in America,” Vitiello said. “Having that additional support is going to make a big difference for them.”