The NFL and its players don't seem to be on the same page.

The league sent out a memo on Saturday morning, laying out the timeline for players of 30 teams (Kansas City Chiefs and Houston Texans can have rookies report earlier) to begin reporting to NFL training camps, beginning with rookies on July 21.

But 49ers stars like George Kittle and Richard Sherman joined a group of NFL players expressing public criticism in the league's lack of transparency regarding health and safety protocols for teams amid the ongoing coronavirus pandemic.

[49ERS INSIDER PODCAST: Listen to the latest episode]

Other NFL stars including former NFL MVP quarterbacks Patrick Mahomes and Drew Brees were among the many stars around the league who voiced their concerns on Twitter Sunday morning.

If the NFL and NFL players association can't reach an agreement on protocols before Monday, rookies from the Chiefs and Texans will be expected to report to their respective facilities on Monday. But lacking an agreement could leave the league open to a grievance, which seems likely given how publicly frustrated players around the NFL appear to be.

NFL Media's Tom Pelissero gave some context as to the particular issues the union and many players seem to be at odds with.

[RELATED: George Kittle questions social distancing in 2020 NFL season]

Sherman is the 49ers' union representative for the NFLPA, and never has been shy about voicing his concerns over the NFL's response to the pandemic. 

Players want an acclimation period, and the NFLPA already recommended canceling the entire preseason in early July to allow for one.

Every American sports league has seen hurdles in their attempts to return to action with the pandemic ongoing, and the NFL is the only one of the four major leagues in the U.S. that hasn't altered the 2020 regular season schedule in any way.

What's clear from today's movement is that NFL players really want to compete in a 2020 season. But they also aren't willing to jeopardize the health and safety of their families unless they feel the league is doing everything in its power to protect them.