(Reuters) -- A federal judge said investors who lost money in Allen Stanford's $7.2 billion Ponzi scheme may pursue most of their lawsuit accusing two large law firms that once represented the now-imprisoned financier of being partially at fault for their losses.

U.S. District Judge David Godbey in Dallas said on Wednesday the roughly 18,000 investors could pursue claims that Chadbourne & Parke and Proskauer Rose knew Stanford was selling fraudulent high-yielding certificates of deposit through his Antigua-based Stanford International Bank, and helped him obstruct a U.S. Securities and Exchange Commission probe.

The judge rejected defense arguments that they deserved immunity under Texas law for work they performed as lawyers. He dismissed claims regarding the sale of older CDs because they were brought too late, and claims accusing Chadbourne and Proskauer of negligently supervising their employees.

Godbey ruled after the U.S. Supreme Court on Feb. 26, 2014 said the lawsuit, which raised claims under state law, could go forward despite protections afforded to defendants under a 1998 federal law, the Securities Litigation Uniform Standards Act.

The lawsuit seeks class action status for investors who suffered an estimated $3 billion to $5 billion of damages, the investors' lawyer Ed Snyder said.

"We are obviously very pleased with the decision," Snyder said in an email.

Stanford's fraud was uncovered in 2009. The law firms plan to defend against the remaining claims.

"We are gratified that the court dismissed a number of the claims as legally deficient," Chadbourne spokesman David Schaefer said. "We look forward to demonstrating that there is no evidence to support the outlandish claims against Chadbourne."

Proskauer said in a statement: "We are pleased that the court dismissed several of the unsubstantiated claims asserted by the plaintiffs and are confident that the remaining claims will ultimately be dismissed."

Stanford, 64, is serving a 110-year prison term following his March 2012 conviction by a federal jury.