A federal judge has warned Justin Baldoni’s lawyers against legal maneuvering that he said may be intended to “promote scandal arising out of unproven potentially libelous statements.”

U.S. District Judge Lewis Liman on Thursday struck from the court’s docket a letter from Bryan Freedman, representing Baldoni, accusing Blake Lively’s legal team of trying to extort Taylor Swift. Freedman claimed that the actress’ lawyer reached out to an attorney at the law firm Venable, which represents the singer, and demanded that Swift issue a public statement in support of the actress under the threat of releasing personal text messages in Lively’s possession if the request was refused.

“Counsel is advised that future misuse of the Court’s docket may be met with sanctions,” Liman wrote.

In the letter filed on Wednesday, Freedman said that a representative for Swift “addressed these inappropriate and apparently extortionate threats” in...