Portland, Oregon-based law firm Tonkon Torp has agreed to pay $18.5 million to resolve litigation accusing it and Sidley Austin, along with accounting firms and banks, of contributing to a Ponzi-like securities fraud by the now-defunct investment fund Aequitas Management LLC.

A proposed class action settlement submitted in Oregon federal court on Monday calls for Tonkon to provide at least $12.9 million to a collection of investors who alleged that the firm and others helped Aequitas mislead them. Court documents also indicate that Tonkon separately agreed to pay nearly $5.6 million to resolve parallel actions brought by individual investors. The settlements, which are subject to court approval, call for Tonkon to pay a total of $18.5 million.