Miller is part of an investigation by the Florida Fish and Wildlife Conservation Commission (FWC) following a recent fishing trip with friends off the coast of Miami.
Miller, who was on a guided fishing tour, landed a 9½-foot hammerhead shark on the outing, posting photos and video of the catch on social media.
People for the Ethical Treatment of Animals (PETA) saw the social media posts and took Miller and company to task promising "to ensure that Miller is held accountable if killing this animal was, as we suspect, illegal."
Following PETA's public rebuke, the FWC began investigating the matter.
"The FWC has received the images and video and is looking into whether or not a violation occurred in this incident," Carol Lyn Parrish, the commission's public information coordinator, said in a statement.
Miller, who posed for a photo with the shark on the boat, later released the animal.
Hammerheads are classified as "Group 3" sharks, according to the commission's website, and the harvesting of them in state waters is a second-degree misdemeanor. In Florida, second-degree misdemeanors are punishable by up to a $500 fine and 60 days in jail, as determined by a judge.
Miller is an avid hunter and fisherman who routinely posts photos and videos of his outdoor endeavors on social media, but he has never received a complaint from a government agency.