WASHINGTON — The Trump administration is seeking new authority to acquire land near the Southern border with Mexico as part of its plan to quickly build immigration barriers, angering activists who said it would violate liberties and endanger the environment as a cost of fulfilling the president’s campaign promise.

The proposed changes are outlined in a border security budget document that was prepared by an agency within the Department of Homeland Security. It was delivered to Congress last week in a funding request asking for $33 billion for border security over the next decade, including $18 billion for a nearly 1,000-mile wall on the Mexican border that President Trump has made a top priority to combat illegal immigration.

The department already has sweeping authority exempting it from a wide range of federal regulations that would otherwise limit its ability to build border fencing and access roads, or add sensors and cameras on land. It is unclear why the requested changes are needed, and a Customs and Border Security spokesman declined to discuss the proposal, “as a matter of policy.”

The budget document said the proposal would “clarify and expand” the Homeland Security secretary’s authority to waive federal laws to quickly build border walls. It also is asking Congress for permission to no longer have to work with other federal agencies, such as the National Park Service, to use lands for security purposes.

