DES MOINES — Iowa’s largest public-employee pension fund says $339 million in assets have been frozen pending a federal investigation into an investment broker-dealer it had ties to.

The Iowa Public Employees Retirement System said the move will not affect monthly benefits paid to its 85,000 pension recipients.

The system also said it has terminated its investment contract with Westridge Capital Management of Santa Barbara, Calif.

The National Futures Association, which regulates its own members, has suspended the trading capabilities of two individuals who are principals in both WG Trading and Westridge Capital Management.

Westridge Capital Management completes transactions through WG Trading, a registered investment broker dealer.

IPERS spokeswoman Julie Economaki said WG Trading is under investigation by the U.S. Commodity Futures Trading Commission and the U.S. Securities and Exchange Commission.

IPERS serves current and former employees and retirees of state, city, and county governments, school districts and other Iowa government agencies. It has more than 312,000 members.

Officials say the funds involved represents about 2 percent of the pension fund’s total assets.

State Treasurer Michael Fitzgerald, also an IPERS board member, said he is troubled about the situation.

“At this point, we don’t know the status of our investments,” he said. “We want to make sure that every penny we have is safe and invested wisely. So when something like this happens I am very concerned.”