In the latest in a long string of legal actions involving Prince's estate, his heirs are accusing Roc Nation of using a fraudulent contract to stream more than 500 of the artist's songs and videos.

Nearly 60 documents, most of them under seal, were filed Friday in U.S. District Court in St. Paul. The plaintiffs, Prince's NPG Records and Music Publishing, are now owned by the estate.

They allege that the defendants, Roc Nation LLC, Aspiro AB, Project Panther Ltd. and WiMP Music AS, fabricated and backdated a contract for the rights to stream Prince's music on Tidal. They say the defendants have failed to cooperate with the estate's request for documentation to prove they have a legitimate contract to use the artist's music.

Since Prince's death from an accidental opioid overdose at his Paisley Park studio in Chanhassen in April 2016, the six heirs to his estate have been in the middle of a protracted legal battle to settle an estate estimated to be worth $100 million to $300 million before taxes.

Tidal is a small, subscription-based music streaming service with an estimated 1 million members, according to court documents. The estate's NPG entities claim to own copyrights on Prince musical compositions and recordings that Tidal exploited without permission or compensation.

Before Prince died, he let Tidal stream some of his music. After his death, the NPG entities allege, Tidal began streaming additional Prince works, including hundreds of works Prince did not authorize and which had never before been available online. Tidal did not communicate with the estate before it began exploiting these works, let alone obtain a license, the NPG entities said.

Tidal claims contractual agreements give it exclusive rights to stream Prince's music.