Some Volkswagen employees worked shortened hours under a warning strike as union and management remain apart on proposed steps to slash costs. Talks over planned plant closures by the German carmaker are expected to continue this month.

Union and management representatives held a fourth round of talks on Monday in Wolfsburg, the northern German city where the firm is headquartered.

They discussed a proposal submitted by the union last month. The plan calls for employees to forego some wages, with money to be channeled into a fund. In return, management would halt plans to shut plants and some other changes. Any plant closure inside Germany would be the first in Volkswagen's 87-year history.

Management rejected the proposal, saying it was not sufficient to ensure a sustainable reduction in costs.

The two sides plan to meet again on December 16.

About 100,000 employees took part in rolling strikes at German plants on December 2. Limited labor actions also unfolded at nine plants on Monday.

Workers are threatening to go on full-scale strikes depending on the outcome of talks.