In papers filed Oct. 7 in New York Supreme Court, the commissioner's office wants Beazley Insurance Co. Inc. to show cause why it shouldn't be required to produce records that could identify the source of leaks.
MLB said Beazley refused to cooperate with baseball's investigation into a story by The Associated Press, published in August 2010, and club documents posted by Deadspin.com, that same month.
Martin Klotz, a lawyer for baseball, said in legal papers that six insurers received the confidential financial information from teams and that all except Beazley cooperated with MLB's investigation.
Baseball said it intends to sue or seek an injunction against those who leaked the information.
The AP story focused on the financial data of the Pittsburgh Pirates. Deadspin published documents from the Pirates, Tampa Bay, Florida, the Los Angeles Angels, Seattle and Texas.
MLB Spokesman Pat Courtney said the league was not commenting.
'We're reviewing the suit and have no further comment at this time," said Lou Ferrara, AP's vice president and managing editor for sports.
Deadspin editor-in-chief A.J. Daulerio declined comment.
"Beazley has cooperated with Major League Baseball," spokeswoman Kimberly Baldoni said. "We conducted an internal investigation, which yielded no evidence that the company or our employees were responsible for the leak. The petition filed has no merit."