Sidley Austin Brown & Wood has been hit by a $155m (£83m) lawsuit over its infamous ‘cookie cutter’ opinion letters, as US lawyers suffer continued fallout from involvement in controversial tax shelters.

The top 10 US firm is being targeted alongside Dallas firm Jenkens & Gilchrist in a suit filed on 5 November in New York by three former clients. Former Sidley tax partner RJ Ruble and former vice chairman Thomas Smith are also named in the case.