An alleged scheme to pay off women to fabricate sexual assault allegations against Special Counsel Robert Mueller has been referred to the FBI for further investigation, according to a spokesman for the special counsel’s office, Peter Carr. “When we learned last week of allegations that women were offered money to make false claims about the Special Counsel, we immediately referred the matter to the FBI for investigation,” Carr said in a statement on Tuesday.

The special counsel’s attention to this scheme—which was brought to the office by a woman claiming she herself had been offered money to make up sexual harassment claims against Mueller—and its decision to release a rare statement about it to reporters indicates the seriousness with which the office is taking the purported scheme to discredit Mueller in the middle of an ongoing investigation.