The Seattle SuperSonics' former owners sued late Tuesday in federal court in Seattle to rescind the 2006 sale of the team.
The lawsuit against the current Oklahoma-based owners is another potential roadblock to efforts to move the team to Oklahoma City.
NBA owners Friday approved the relocation.
The current owners already face a federal trial in Seattle on June 16. The city of Seattle is trying to force them to play in Seattle for two more years, the length of the team's lease at Key Arena.
Former owner Howard Schultz said last week through an attorney that he planned to sue. He claims he was lied to when the new owners said they would work to keep the team in Washington.
An attorney for the current owners, as well as a spokesman, had no comment Tuesday.
Sonics Chairman Clay Bennett said Friday he was disappointed Schultz was going to sue.
"Well, I operated in good faith,” Bennett said. "I was disappointed because I've had a nice relationship with Howard, and I have not spoken with him about this ... issue. ... I made a commitment to him personally, as well, that was meaningful to me and I hail to that commitment.”
New lawsuit against Sonics owners