SuperMarksBros.
Formerly Fiedler for MVP
They are not investigating the specific decision. They are investigating to determine if the protocol requirements are satisfactory and sufficient. You imply they are investigating the organization for wrongdoing, when that is not at all the case.
I'm not even sure the NFLPA has standing to force the issue legally, if there is no complaint by the affected member parties.
NFLPA begins investigation into handling of Tua Tagovailoa’s concussion examination
Quarterback was visibly staggered after a play but returned to the game
www.sbnation.com
"The NFLPA is initiating an investigation into the handling of #Dolphins QB Tua Tagovailoa’s concussion check during their game against the #Bills today in Miami, per source."