SYDNEY, Australia (AP) — Actor Sylvester Stallone pleaded guilty Tuesday to bringing vials of a restricted muscle-building hormone into Australia.

Lawyers for the 60-year-old star of the "Rocky" and "Rambo" movies entered the guilty plea on behalf of the actor, who did not appear before Sydney's Downing Center Local Court.

Stallone was accused of bringing a banned substance into Australia after a customs search of his luggage during a Feb. 16 visit to Sydney revealed 48 vials of the human growth hormone product, Jintropin.

Human growth hormone, a naturally occurring substance that can be replicated synthetically and is used to build muscle mass, is considered a performance enhancing drug in Australia, and it cannot be imported without a permit from the national drug regulator, the Therapeutic Goods Administration.

Stallone faces a maximum penalty of a $22,000 fine. Sentencing information was not released, and Stallone's lawyers made no immediately comment.

Prosecution documents handed to the court in March said Stallone had marked "No" on a customs declaration card that asked if he was bringing into Australia restricted or prohibited goods "such as medicines, steroids, firearms, weapons, or any kind of illicit drugs."

During his visit to Australia, Stallone shrugged off the airport incident.

"It was just a minor misunderstanding," Stallone told reporters "They were just doing their jobs. I just didn't understand some of the rules here."