SEPTA Transit Police Chief Thomas J. Nestel III confirmed that the investigation is to determine if the officers engaged in criminal behavior or violated departmental policies, and not whether they attended the protest.
"It's their first amendment right. They can do that if they chose, but what we're concerned about is whether they were involved in the criminal activity," said Nestel Tuesday night.
Troy Parham, the vice president of SEPTA's police union, tells Action News that of the seven under investigation, two are supervisors and five others are officers.
"I feel confident that my officers weren't involved in anything illegal," he says.
The investigation comes just days after the Philadelphia Police Department announced a similar probe into a detective who reportedly attended the Trump rally on January 6.
SEE ALSO: Trump issues emergency declaration for DC ahead of Biden inauguration
Sources tell Action News that the police detective works in the recruitment division and is tasked with screening new recruits to make sure they are fit to serve. Part of the detective's job involves screening the social media accounts of those recruits.
Hundreds of pro-Trump supporters stormed the US Capitol building as Congress was voting to certify President-elect Joe Biden's victory. Five people died including a Capitol police officer. Benjamin Phillips of Ringtown, Pennsylvania also died after suffering an apparent medical emergency.
SEE ALSO: Philadelphia detective under investigation after allegedly attending Trump rally in DC
Across the country, police and fire departments are opening probes into officers who attended the rally. In Seattle, Western Pennsylvania and Texas, officers are under investigation to determine if they took part in the violence.
Dozens of people have been arrested in connection with the protest and riot, including 12 people from Pennsylvania and one South Jersey man.