US grocers Kroger, Albertsons, and Safeway have ratified a new contract with workers in California that ends the longest-running grocery strike in US history.

The contract covering 70,000 members of the United Food and Commercial Workers Union at the three supermarket chains was approved by 86% of those voting.

The strike affected 900 stores and is believed to have cost the chains more than $1bn.

The conflict arose when the supermarkets said that could no longer afford to pay for benefits such as health care without contributions from employees in the face of competition from non-union rivals like Wal-Mart.

Workers are expected to start returning to work this week.