H&R Block, the US tax preparer, is facing a tough proxy fight after two big shareholders threw their weight behind the dissident board slate put up by Richard Breeden, a former chairman of the Securities and Exchange Commission.

Ariel Capital Management, which holds just over 5 per cent cent of H&R Block, said on Friday: “It is the present intention to vote the shares of H&R Block held on behalf of... clients in favour of the three board candidates nominated by Breeden Partners.”