Shares in US chocolate producer Hershey Foods dropped off by 4% one day after employees voted to reject a new contract deal offered by management in favour of strike action.

Some 3,000 staff at Hershey facilities in Pennsylvania, accounting for a fifth of the workforce, have been offered a new contract after a four-year contract expired in November. It is believed the conflicted clauses concern wages and healthcare costs for current and retired workers.

The two plants together make around 40% of Hershey's output.

Shares in Hershay fell 2.6% to US$68.1 in mid-afternoon New York Stock Exchange trading. Earlier they had dipped as low as US$67.3, reported Reuters.