The Department of Homeland Security has imposed new limits on visits by members of Congress and their staff to immigration enforcement facilities, intensifying a conflict between federal immigration officials and Democratic lawmakers over the separation of powers.

Under federal law, members of Congress can make unannounced oversight visits to immigration facilities that “detain or otherwise house aliens.” Lawmakers are not required to provide “prior notice of the intent to enter a facility” to conduct oversight, though members of their staff must request a visit at least 24 hours in advance.

But in guidance released this month, Immigration and Customs Enforcement asks members of Congress to give at least 72 hours notice for a visit to its facilities. Asked about the policy, a spokeswoman for the Department of Homeland Security, which oversees ICE, went even further, suggesting that federal officials would not be allowed entry unless they provided a week’s notice.

“A week is sufficient to ensure no intrusion on the president’s constitutional authority,” the spokeswoman, Tricia McLaughlin, said in a statement. She added that “any request to shorten that time must be approved” by the homeland security secretary, Kristi Noem.

As Democratic lawmakers criticize the Trump administration’s immigration crackdown and accuse officials of abusing executive power, ICE facilities have become the battlegrounds of a political showdown.

Members of Congress have repeatedly been denied access to ICE facilities this month as they try to conduct oversight visits, and some of them have been involved in high-profile clashes with immigration officials.