The NFL means business when it comes to its COVID-19 protocols for the 2021 season, especially when it comes to vaccinations. But some of the league's stars are pushing back.

The league, which opened its preseason last week, is requiring its “Tier 1” employees — coaches, front-office executives, equipment managers and scouts — to be vaccinated, but it is only encouraging it for players.

Ninety percent of players have received at least one vaccine dose, NFL spokesman Brian McCarthy said last week. On 27 of the 32 teams, at least 85% of players have been at least partially vaccinated.

Those rates exceed the national average of 71% of adults who have been given at least one shot.

In a memo to teams last month, Commissioner Roger Goodell made it clear the NFL will have little patience for outbreaks among the unvaccinated. Among the policies, a team could face a forfeit if it cannot play due to a COVID-19 cluster caused by unvaccinated players or staff and the league cannot reschedule the game. Vaccinated players also won’t be required to quarantine if deemed a close contact to an infected player.

“These operating principles are designed to allow us to play a full season in a safe and responsible way and address possible competitive or financial issues fairly,” Goodell wrote in the memo. “While there is no question that health conditions have improved from last year, we cannot be complacent or simply assume that we will be able to play without interruption — either due to Covid outbreaks among our clubs or outbreaks that occur within the larger community.”

While players are not being required to be vaccinated, some say they feel the league is pressuring them.

“It is no secret that they've been trying to push it on unvaccinated guys,” Dolphins tight end Adam Shaheen told reporters Saturday. “I'm going to continue to go through the protocols of the unvaccinated that they make me do. I'm not going to get fined. But they are not going to strong-arm me into doing something for more freedom when this is such a changing atmosphere and they are already taking away freedoms of unvaccinated guys."

Shaheen was just removed from the Dolphins’ COVID-19 reserve list but said he personally did not test positive for the coronavirus.

After the NFL announced its COVID policy for the upcoming season, Arizona Cardinals All-Pro wide receiver DeAndre Hopkins posted, then deleted, a tweet saying, “Being put in a position to hurt my team because I don’t want to partake in the vaccine is making me question my future in the @Nfl.”

Buffalo Bills wide receiver Cole Beasley accused the NFL of withholding information from players in order to sway them into getting inoculated. 

“When dealing with a player’s health and safety, there should be complete transparency regarding information that is vital in the decision-making process,” Beasley said. “Without having all the proper information, a player can feel misguided and unsure about a very personal choice.”

While Beasley says he’s “pro choice” when its come the vaccine, he released a rap song last month that suggests he’s firmly opposed to the shot.

“Ain’t no vaccination for me, only evacuation save ’em homie,” he raps in the song “Heavy 1s.”

Meanwhile in Minnesota, assistant coach Rick Dennison is sitting out the season after refusing to get vaccinated. He'll instead serve as a senior adviser to the team and work remotely.

And Vikings Pro Bowl quarterback Kirk Cousins would not say last week if he’s been vaccinated. He did, however, make headlines for saying he’d thought about surrounding himself with plexiglass to avoid close contacts with potentially infected people.

Cousins was one of three Vikings quarterbacks who was recently placed on the team’s COVID-19 reserve list after teammate Kellen Mond reportedly test positive, leaving just one eligible QB available for practice.

Some coaches, including Cousin’s, have expressed their frustration with the vaccine holdouts. 

"Going through all the things you had to do last year with masks, protocol, traveling, can't leave for a day, can't go out and see your family and all the things, can't go out to dinner on the road, have to wear masks on the plane, all that stuff — it was just difficult," Vikings coach Mike Zimmer told ESPN last week. "I just don't understand. I just don't understand. I think we could put this thing to bed if we all do this. But it is what it is."

Washington Football Team coach Ron Rivera, who battled skin cancer last year, said he was “beyond frustrated” with his team’s vaccination rate, which had been the league’s lowest.

“Part of the reason I walk in with a mask on is I’m immune-deficient,” Rivera said. “So with this new (delta) variant, who knows? So, when I’m in a group, and the group’s not vaccinated, or there’s a mixture, I put the mask on, and I do that for health reasons because nobody really knows. And, so I have to do that. And I just wish and I hope that our guys can understand that.”

Rivera’s players seem to have taken his message to heart, as Washington’s rate of players who have been partially vaccinated jumped from 60% to 84% in about a week, The Washington Post reported.

The pandemic caused its share of headaches for the NFL last season. In addition to many players — including stars such as Ben Roethlisberger and Alvin Kamara — missing games while on the COVID-19 reserve list, outbreaks on the Tennessee Titans, New England Patriots and Baltimore Ravens forced contests to be rescheduled. And the Denver Broncos were forced to play a game with no true quarterback because one QB tested positive and the others were ruled close contacts.