While the NFL was celebrating another strong slate of Sunday games, federal agents were interviewing doctors and trailers for several NFL teams to investigate possible illegal painkiller distribution.

The Washington Post reports that the Drug Enforcement Administration agents were acting on the suspicion that NFL medical staffs were handing out drugs illegally. The agents also only inspected away team buses, so the work was done in cooperation with the Transportation Security Administration.

While the DEA didn’t say what teams were inspected, the San Francisco 49ers, who were in New Jersey to play the New York Jets, confirmed that they were one of the teams. The other two were the Seattle Seahawks, who were in Kansas City, and the Tampa Bay Buccaneers, who were at the Baltimore-Washington International airport following their game at the Washington Redskins.

As CBS Sports noted, the Bucs announced that they were searched on their way to BWI and were completely cooperative.

The inspections were not previously announced. A source for CBS Sports said that they came about because the DEA had reason to believe that the Controlled Substances Act was being violated and not followed by the NFL. The DEA was asking teams for prescriptions, since there are concerns that teams were handing out painkillers and other prescription drugs without documentation.

While only three teams were inspected on Sunday, this does not mean that the DEA is specifically only investigating them. The Post’s source said that the investigation does include all 32 teams in the league.

The investigation was sparked by a class-action lawsuit that over 1,300 former NFL players filed against the league, claiming that the medical staffs often break laws by providing addictive narcotics to players so they can play through injuries. The suit was filed back in May 2013.

image of NFL commissioner Roger Goodell courtesy of Dara Kushner/INFphoto.com