Investors who sued Proskauer Rose in August accusing one of its partners of involvement in Stanford Financial Group’s alleged Ponzi scheme have added Chadbourne & Parke as a defendant.

The class action alleges that attorney Thomas V. Sjoblom, while he worked at New York-based Chadbourne & Parke and later at New York’s Proskauer Rose, participated in a $7 billion investment fraud orchestrated by the Texas company.