U.S. Sen. Ron Wyden (D-Ore.), who sits on the Senate Intelligence Committee, expressed concern following WW's June 15 report about a plane with links to the U.S. Marshals Service that circled above Portland protesters for hours on Saturday.

"This reporting by Willamette Week raises troubling questions about law enforcement tactics in Portland that mirror concerns I expressed last week to the Trump administration about federal authorities targeting and surveilling protesters exercising their First Amendment rights," Wyden said in a statement. "I will not stop pressing federal law enforcement to respond to all of these serious questions arising in real time about surveillance abuse during constitutionally protected protests."

On Saturday, as thousands gathered in the city to protest police brutality against black Americans, an aircraft circled above Portland for three hours. The aircraft's tail number was registered to a company that has been linked through public records to the U.S. Marshals Service. Reached by phone Monday, the agency declined to acknowledge whether it owns the aircraft that circled the protests.

The flight path of an aircraft linked to the U.S. Marshals Service that circled downtown Portland for three hours as protests ensued on Saturday. (Flightaware.com)
The flight path of an aircraft linked to the U.S. Marshals Service that circled downtown Portland for three hours as protests ensued on Saturday. (Flightaware.com)

Just three days earlier, Wyden had sent the U.S. Department of Justice questions about how it was using aircraft to surveil protesters.

In a letter to U.S. Attorney General William Barr on June 10, Wyden and U.S.  Reps. Anna Eshoo and Ted Lieu, both Democrats from California, called on the DOJ to release information related to nationwide surveillance of protesters.

The letter raises concerns about law enforcement agencies, including the U.S. Marshals Service, that use Cessna airplanes equipped with cell-site simulators that can mimic cell towers as the plane circles repeatedly over a particular area. CSS, also called "dirtboxes," can collect and aggregate data from thousands of people within the plane's scope. Since at least 2014, the U.S. Marshals Service has used this tactic to collect data, The Wall Street Journal reported.

"We write with great concern about law enforcement agencies targeting and surveilling protesters who are engaged in constitutionally protected expressions of free speech," the legislators wrote in the letter. "Given the lack of transparency and accountability regarding the transfer of this technology between and among agencies, we remain deeply concerned about its potential for surveillance abuse against innocent and vulnerable populations exercising their First Amendment rights."