Vital car-parts maker Robert Bosch is to lay off 170 manufacturing workers in the latest blow to the car industry.

Workers were informed this morning of the news, after which about 200 assembled near the main gates of Robert Bosch in Centre Road, Clayton.

Australian Manufacturing Workers Union national secretary Dave Oliver said the company had been unreasonable and had recently asked workers to effectively take a 50% pay cut - a claim rejected by the company.

"A lot of people can't sustain that [the pay cut]," he said.

While conceding the industry was under considerable pressure, he said Robert Bosch had been unwilling to share the pain.