Adam Schefter and Damien Woody react to the NFL investigating the Ravens for running a full pads session during rookie minicamp. (1:17)

The Baltimore Ravens will be investigated for using full pads at a recent rookie minicamp, which is a violation of the collective bargaining agreement, a league source said.

A Ravens official said the team is unaware of any investigation but explained there was a five-minute period on May 6 when rookies and first-year players suited up in pads during a non-contact punt protection drill. The team believed rookie minicamp didn't fall under the same rules as the organized team activities and immediately pulled players off the field once it received clarification from players' union representative Benjamin Watson, according to a Ravens official.

Teams are not allowed to suit up in full pads until training camp. Offseason rules have become more strict since 2011, when the latest CBA was passed.

For an investigation to begin, a player has to report a violation to the union or league. A Ravens official said everything can be verified because all practices were taped.

In 2010, the Ravens were disciplined by the NFL after six players complained to the players' union about late meetings and two others reported being held too long on the field after practice. Baltimore had to cancel the final week of offseason workouts.