Striking workers at two key General Motors parts plants in Michigan overwhelmingly ratified a deal to end the carmaker's longest labour dispute in nearly 30 years, union officials said.

At GM's Metal Center, 90 percent of the 3,400 workers who had walked out on June 5th voted to return to work, while at the Delphi East parts plant, 76 per cent of the 5,800 workers on strike since June 11th voted to return to work, a United Auto Workers (UAW) spokesman announced.

The vote brought to an end the longest and most contentious labour dispute in the United States since a 67-day UAW strike against GM in 1970.

The strikes had virtually crippled GM's North American operations, costing the car maker an estimated $2.5 billion in lost production.