The plant stopped operating after the walkout.
Staff on the afternoon shift also walked out shortly after they arrived for work at 1pm.
The staff left their stations following comments from Carl Peter Forster, GM European president. Forster said the only way forward at Ellesmere Port was to cut one shift from the plant, according to the unions.
"We would have expected better from such a senior executive of the company," said Roger Maddison of the Amicus union.
"His comments are extremely unhelpful during critical ongoing negotiations between the company and trade unions in Germany."
"British car workers are among the best in Europe, but they're the easiest to sack," said Tony Woodley, general secretary of the Transport and General Workers Union.
"These decisions are not led by business logic, but by the fact that our laws don't protect our workers."