July 16 (Reuters) - Medical device maker Masimo Corp on Tuesday said it has started litigation against Politan Capital in a California federal court, seeking to force the activist investor to correct "material misstatements and omissions" in its proxy materials.

Masimo is locked in a proxy contest with Politan, which has long criticized the California-based company's board oversight and expressed concerns about its purchase of Sound United.

Quentin Koffey-owned Politan owns nearly 9% stake in Masimo and has been seeking two board seats in the company's five-member board.

Masimo has also postponed its annual shareholder meeting to Sept. 19 from July 25 earlier, the company said in a statement.

Politan did not immediately respond to a Reuters request for comment. (Reporting by Surbhi Misra in Bengaluru; Editing by Rashmi Aich)