SAN DIEGO, Calif. – A Hillshire Brands Co. shareholder filed a lawsuit to stop Tyson Foods Inc.'s acquisition of Hillshire, while another law firm is investigating the transaction.

The plaintiff claims Hillshire executives breached their fiduciary duties by agreeing to sell the company to Tyson Foods "too cheaply via an unfair process", according to a statement from the Shareholders Foundation Inc., San Diego. The company is a portfolio monitoring service specializing in securities class action and other legal actions.

Stevenson, Maryland-based Brower Piven, a securities litigation law firm, recently announced the firm's intention to investigate possible breaches of fiduciary duty and other violations by the Hillshire board.

Springdale, Arkansas-based Tyson Foods agreed to acquire all outstanding shares of Hillshire Brands for $63 per share. The all-cash transaction is valued at approximately $8.55 billion.