The NFL Players Association wrote a letter calling for the "immediate replacement and ban" of slit-film turf fields throughout the league.

The league uses three types of turf: slit-firm, dual fiber, and monofilament, but it's the slit-firm surface that has proven players to miss more time due to injuries, which happen at an increased rate on it as well.

"Advocating for safer working conditions is a core job of our union, and there are few greater examples of this than raising the standards of the fields we practice and play on," NFLPA President JC Tretter wrote on Saturday.