Chemicals and mining workers union IG BCE is demanding a 5.5 percent pay rise for energy employees, including those at E.ON's units PreussenElektra and Avacon as well as power network operator Tennet .

Workers at grid operator Avacon will stage a strike all day on Monday and staff at nuclear unit PreussenElektra will follow a week later with strikes and demonstrations at the Grohnde nuclear plant, in Lower Saxony, IG BCE said on Friday.

The union said employers had offered to raise salaries by 2.1 percent over 18 months at the latest round of talks last month, but chief negotiator Holger Nieden said that did not take the good economic situation into account.

"The offer is completely insufficient. It's time to increase the pressure," he said.

Trade union Verdi, which is also negotiating for energy workers, is calling for a 6 percent wage increase. It said the next round of talks was scheduled for Feb. 27.

A spokesman for E.ON said the group was confident a fair and balanced wage deal could be reached that would adequately reflect employee interests, the company's economic situation as well the competitive environment.

Earlier this month, industrial workers in southwestern Germany struck a hard-fought deal with employers on pay and working hours, setting a benchmark for millions of workers across Europe's largest economy.

That agreement, between labour union IG Metall and the Suedwestmetall employers' federation, foresees a 4.3 percent raise from April and other payments spread over 27 months.

(Reporting by Christoph Steitz and Matthias Inverardi; Editing by Victoria Bryan and Susan Fenton)