Federal investigators are examining nearly four dozen hedge funds, asset managers and other investment firms to determine whether they violated insider-trading rules after receiving a tip from a Washington research firm.

In a new court filing, the Securities and Exchange Commission said it is looking at 44 investment funds and other entities, including "some of the largest hedge funds and asset management advisors in the nation," as part of its probe into whether anyone broke the law by buying health-insurance stocks in April 2013 ahead of a government announcement that benefited the firms.