Texas law firms Strasburger & Price and Castillo Snyder opened a new front Thursday in the legal battles over Stanford Financial Group, the company R. Allen Stanford allegedly used to chisel billions of dollars from unwitting investors. In a federal class action filed in Dallas on behalf of Mexican investors, the lawyers accused U.K. insurance giant Willis Group Holdings and smaller Texas insurance broker Bowen, Miclette & Britt of aiding Stanford’s alleged fraud by vouching for his investments.

The complaint states that the defendants gave Stanford Financial “safety and soundness” letters designed to help it market its investments. “Willis and BMB crossed the line from being mere insurance brokers for the Stanford Financial Group,” the complaint alleges. “In creating and submitting these letters into the stream of commerce, [the defendants] actively and materially aided Stanford Financial to perpetrate the massive Ponzi scheme now alleged by the SEC.” The plaintiffs are seeking damages of more than $1 billion.