SMITHFIELD -- Activists who accuse Aero Contractors Ltd. of doing the federal government’s dirty work picked up trash outside the company’s headquarters on Saturday to symbolize the legal “cleanup” they have been unable to accomplish for years.

N.C. Stop Torture Now has accused the company of using the Johnston County Airport to operate a flying taxi service for paramilitary teams that pick up terrorism suspects in one country and fly them to another for interrogation. Through this process, called extraordinary rendition, the government is questioning suspects using torture techniques prohibited under various international treaties and laws, members of the group say.

Allyson Caison, a leader of N.C. Stop Torture Now, asked the state Department of Transportation last year if the group could take on cleanup of Swift Creek Road in Smithfield through its Adopt-A-Highway program. Swift Creek Road runs in front of the Johnston County Airport and the headquarters of Aero Contractors.

The application was approved, and the DOT installed signs just before Christmas indicating the group’s responsibility for cleanup along the 2.5 miles of Swift Creek Road that run between Cleveland Road and U.S. 70 Business.

“I care about the county, I care about the rule of law, and I care about the environment. This was a perfect match,” Caison said Saturday morning during a brief gathering before volunteers set out with their trash bags.

About two dozen supporters came out for the cleanup, donning bright orange vests and fanning out along the highway shoulders. There was plenty of work for them; the county landfill is on Swift Creek Road, generating considerable traffic, and it appears that some of what’s intended for the dump is dropped along the highway before it gets there.

Aero Contractors could not be reached for comment Saturday. The company has declined to comment on the anti-torture group’s allegations in the past.

N.C. Stop Torture Now has pressed for years to get local, state or federal officials to investigate Aero Contractors’ activities from the airport. In January 2012, the Immigration and Human Rights Policy Clinic of the UNC School of Law issued a report that found the company had supplied the CIA with aircraft and crews, and that company flights coincided with the known movement of certain detainees from place to place.

Eventually, the public will demand an accounting of Aero’s work and the government policies it represents, said Christina Cowger, another leader of N.C. Stop Torture Now. Until that happens, she said, the group will keep pressing.

“State and county officials think we’ll go away,” she said. “We’re not going away.”