Actress Allison Mack leaves Brooklyn federal court in New York earlier this month. Mack pleaded guilty to racketeering charges in a case involving a cult-like group based in upstate New York. File picture: Mark Lennihan/AP

New York - "Smallville" actress Allison Mack may testify against the alleged leader of an Albany, New York-based sex cult whose followers had "dozens" of abortions at his behest, it was revealed in court Monday.

The revelations were made during jury selection in the trial of NXIVM founder Keith Raniere, whose supposed self-help group fronted a demented sex sect in which victims were branded, tortured and sexually abused, federal prosecutors say.

Raniere, 58, is headed to trial by himself in early May after his co-defendants, including Mack, 35, and Seagram's liquor heiress Clare Bronfman, 40, pleaded guilty to crimes relating to the group's dark doings.

Monday was the first day of jury selection at what is expected to be the cult leader's salacious trial.

The fact that Mack may testify came out during a discussion about a prospective juror who said he had read about the case and specifically recalled "writings" related to the actress' involvement.

"I think that person might testify," Raniere's lawyer Marc Agnifilo said during a discussion outside the juror's presence and in response to the man's comment about Mack.

Several candidates said they were staunchly opposed to abortion in response to a question posed in a screening questionnaire.

Raniere's use of abortion as a birth control tactic is expected to be an ongoing theme at the trial in Brooklyn Federal Court.

"There are a lot of abortions in this case. Dozens," Agnifilo said at a sidebar during questioning of the would-be panelist.

"As part and parcel of his desire to have sex with lots of women, he used abortions cavalierly," he added.

US District Court Judge Nicholas Garaufis previously ordered that the jury remain anonymous.

Raniere, whose trial is expected to last six weeks, is charged with a host of federal statute violations including child pornography and having sex with a 15-year-old victim in his charge.