The Marlins were allowed to have beards the past two years but Mattingly changed the organization's policy after being hired.
"Guys will whine," Mattingly told reporters Sunday. "Some guys like it; some guys won't. As long as we're consistent, I think it's not that big of a deal."
It was a stunning change to the players, many of whom had to shave off beards or goatees either before or upon arriving at spring training.
"Initially not too many guys were happy about it," said reliever Mike Dunn, who shaved off his goatee before reporting to camp. "You can fight it, or you don't. Obviously I shaved, so it's OK."
Adding intrigue to Mattingly's policy is that the Los Angeles Dodgers allowed facial hair in his five seasons as their manager.
Also, Mattingly had a mustache as a player for the New York Yankees. He once was benched in 1991 for refusing to cut his hair.
Marlins starting pitcher Jose Fernandez blended humor in with seriousness to his response about the new policy.
"I'm afraid I'm going to look 16," Fernandez said with a smile. "But it's not a big deal. Whatever the rules are, we're going to follow them."