The IG Metall union has called on Mercedes-Benz workers across Germany to protest against a tightening of the carmaker's cost-cutting measures, with rallies planned at several sites on Friday.

Rallies are to be held at the Sindelfingen and Untertürkheim sites in Stuttgart. Further actions are also planned in Rastatt, Kuppenheim, Bremen, Berlin, Hamburg, Dusseldorf, Ludwigsfelde and Germersheim, the union's Stuttgart branch said on Wednesday.

The protests come in response to a tightening of the austerity programme at the Stuttgart-based carmaker. "From IG Metall's perspective, these measures are directed one-sidedly against employees and call into question key collectively agreed achievements," the union said.

In a letter to employees in Germany sent at the end of last week, the board said the company must "continue to reduce costs at full speed" in order to remain competitive on product pricing. "Despite all our efforts, the situation in Germany today is dramatic," the letter said.

Around 90,000 of the roughly 108,000 employees in Germany will not receive an expected collectively agreed special payment, amounting to 18.4% of their monthly salary, in July as an immediate measure. The letter said the payment would be deferred to next year.

According to the IG Metall website, the special payment can be deferred or suspended at companies facing economic difficulties.

"At Mercedes-Benz, we will radically accelerate processes and streamline established structures," the letter continued. "The most direct and, in our view, fairest way forward is for us to work more for the same pay across all areas."

The board said discussions would be held with employee representatives over the coming weeks and months on how to secure the company's long-term viability in Germany.