Buck was in court on Thursday to face felony charges of maintaining a drug house, battery causing serious injury and administering methamphetamine. His arraignment for those charges was postponed until October 11.
Buck is accused of injecting a 37-year-old man with methamphetamine at his West Hollywood apartment on September 11, the Los Angeles County District Attorney's Office said. The man suffered a nonfatal overdose.
Two other men have been found dead in Buck's home over the past few years due to methamphetamine overdoses.
Buck's attorney, Seymour Amster, told reporters at the courthouse that he was just made aware of the federal charges and didn't have any additional details.
"This is a case that there have been a lot of activists' interaction on it, thinking that charges should have been brought before there were," Amster said.
"We will fight this case vigorously, but I'm not so sure legitimately there was ever enough evidence to ever cause this case to be filed until recently," he added.
Buck remains in custody on $4 million bail.