CHICAGO (REUTERS) - The US Securities and Exchange Commission has launched an inquiry into whether high-speed trader Infinium Capital Management violated federal securities laws, according to a SEC letter obtained by Reuters.

The SEC has sought documents and recordings related to a lawsuit that former Infinium employees brought against the firm in January, the Feb. 27 letter said.

The lawsuit, filed in U.S. District Court in Chicago, alleged Infinium and company executives committed "securities fraud" by tricking the employees into investing millions of dollars into the firm while hiding financial troubles.

"This inquiry is a non-public, fact-finding inquiry," the SEC letter said. "We are trying to determine whether there have been any violations of the federal securities laws." The SEC does not confirm the existence of investigations as a matter of policy, a spokesman said.

Infinium said on Thursday it was actively winding down the company and had sold some assets to currency broker FXCM Inc . A spokeswoman for FXCM could not be reached immediately for comment.