The NFLPA is pushing for an all-virtual offseason ahead of the 2021 season.
"We’ve been telling them it’s voluntary and we’re not gonna go," Tretter said.
The players' union also requested virtually conducted mandatory minicamps in June as the COVID-19 pandemic continues.
About 300 of the NFL's 2,500 players could miss out on workout-related bonuses if they skip OTAs, Pelissero added.
The league previously sent a memo in March to prepare players for the beginning of virtual offseason programs on April 19, adding that it didn't expect an all-virtual workout schedule similar to what players experienced in 2020.
The NFL has also stated it will not mandate COVID-19 vaccines but did indicate the league could ease pandemic restrictions if teams reach a certain rate of vaccination among staff and players.