A pair of mortgage fraud investigations in Arizona and Nevada has given rise to an angry spat between two high powered Washington, D.C., law firms.

On Monday, Cohen, Milstein, Sellers & Toll partner Linda Singer fired off a terse letter to BuckleySandler, the year-old firm headed by longtime Skadden, Arps, Slate, Meagher & Flom partner Andrew Sandler, demanding that its lawyers “correct the knowingly false assertions” contained in a federal lawsuit it filed last week. The complaint, filed in the U.S. District Court for the District of Columbia on behalf of the nation’s largest homebuilder, Pulte Homes, asks a judge to bar the Arizona and Nevada state attorneys general from employing Cohen Milstein to investigate potential mortgage fraud cases against the housing giant.