The two parties are looking into offensive tackle Trent Brown possibly failing to consistently wear his tracking device prior to testing positive, and a video of offensive linemen in close contact while not wearing masks.
It's standard procedure for the NFL and the union to review any team after multiple positive tests, Pelissero adds.
Brown was placed on the COVID-19 list Wednesday, joining cornerback Damon Arnette, who landed on the list Monday. The Raiders also sent home their entire starting offensive line after the unit's close contact with Brown.
Safety Johnathan Abram was sent away too as a result of contact tracing.
The Raiders will place the remainder of their starting offensive line and Abram on the COVID-19 list, according to ESPN's Paul Gutierrez. They could play this week but will need to quarantine for five days before passing a COVID-19 test Sunday.
Las Vegas is scheduled to take on the Tampa Bay Buccaneers in Week 7.