Western European workers at General Motors are putting pressure on the US carmaker over its threat to shut an assembly plant in Portugal.
GM's German workers are worried about job cuts
Staff at the Azambuja plant in central Portugal briefly downed tools, while those at four German factories are due to hold protests and ban overtime.
GM has deferred a decision to close the Portuguese plant, giving the government time to produce a rescue plan.
Workers also fear that GM is seeking more cutbacks across western Europe.
GM recently broke ground at a major new production site outside St.Petersburg in Russia, and is in talks about opening a joint-venture facility near Warsaw in Poland.
It has said that it costs 500 euros (£342) more per vehicle to produce its Combo delivery vans in Portugal than at other potential manufacturing sites.
Last week it told the 1,100 Azambuja workers that production would be shifted to Zaragoza in Spain, but has now deferred the decision for five weeks after the Portuguese government stepped in.
Workers for GM's German division, Opel, are holding a protest at the Kaiserslauten plant on Monday, with another due at Ruesselsheim on Tuesday. Staff at Opel's Eisenach factory are refusing to work overtime.
"Workers want to show their solidarity with their Portuguese colleagues and try to prevent GM Europe from moving jobs and production to the East," said a spokesman for the IG Metall union.
Uncertainty also surrounds the carmaker's Ellesmere Port plant in northwest England, which makes the Astra car, a model for which GM expects demand to decline.
It announced the loss of about 900 jobs there back in May, and bosses have hinted that the UK market is "more capable" of absorbing job cuts.
GM Europe is in the process of cutting about 12,000 jobs as it looks to reduce costs in a region where it last made an annual profit in 1999.
The company is also engaged in a series of large-scale job cuts in the United States, in attempt to regain profitability in the face of increasing competition from Japanese carmarkers.
GM, which is still the largest US carmaker, made a loss of $10bn in 2005.