A propane supplier is suing DLA Piper for breaching fiduciary duties and “double-dealing,” citing an emailed invoice that the law firm mistakenly sent to the company last year revealing a conflict.

Ferrellgas and parent company Ferrellgas Partners, represented by Squire Patton Boggs, filed suit against DLA on Tuesday, alleging the mistaken email showed the law firm represented adverse interests engaged in a hostile bid to take over the company.