By Devan Cole, CNN

(CNN) -- Oregon's two Democratic senators are pushing legislation that aims to scale back the use of federal law enforcement agents against protesters in Portland and other cities, as well as prevent agents from making arrests without displaying clear identification.

The legislation, which is being proposed by Oregon Sen. Jeff Merkley as an amendment to a National Defense Authorization Act budget bill the Senate is considering, would require all federal agents making arrests or assisting in crowd control to "at all times display identifying information in a clearly visible fashion," including their agency's name and their last name. Agents would also be prohibited from using unmarked vehicles during arrests.

The proposal would also limit the scope of federal agents' jurisdiction to federal property and "the sidewalk and the public street immediately adjacent to any Federal building or property." A request by both a state governor and a city's mayor would be needed before agents could be deployed elsewhere, according to the legislation. It would make it illegal for federal agents to make arrests if they're in violation of the legislation's provisions.

The Democratic-backed resolution poses an uphill battle to be included in the NDAA, and it's unclear if Democrats plan to do anything to block or slow down the overall NDAA if Republicans object to the amendment given the importance and widespread bipartisan support for the authorization act.

Federal agents, including ones from the Department of Homeland Security's immigration agencies, have been deployed to Portland to assist the Federal Protective Service, which is responsible for protecting federal government facilities and their employees and visitors, amid protests that were spurred by the killing of George Floyd at the hands of Minneapolis police officers.

Recent videos from the scenes of the protests show DHS personnel arresting protesters and putting them in unmarked SUVs. In one such video that was shared on Twitter by Merkley, two masked, camouflaged individuals with generic "police" patches detain a person dressed in a black outfit and place them in an unmarked van before driving away. US Customs and Border Protection has identified the officers as belonging to that agency, and indicated the man was wanted for questioning regarding a possible crime. However, a DHS official said he was later released.

"What we have seen in the last 10 days in Portland has been horrific and unconscionable," Merkley said in a statement. "Federal forces have shot an unarmed protester in the head with impact munitions, and paramilitary forces in camouflage have been grabbing people off the streets and putting them into unmarked vans."

"These are the actions of an authoritarian regime, not a democratic republic. This gross violation of Americans' civil rights must end immediately."

Merkley, Oregon's Democratic governor and the mayor of Portland have all called for the federal agents to leave the city, which has seen protests for more than 50 nights.