Nokia, the world's top cellphone maker, said it will start talks with Finnish employees over the company's new strategy, which unions fear could cost more than 5,000 jobs in the Nordic country.

Nokia last month announced a strategy overhaul, dumping its own software platforms and saying it would start to use Microsoft's Windows Phone.

Shares in Nokia, the national champion in Finland, have dropped more than 20 percent since.

Nokia said topics to be discussed include the planned changes in organization and work arrangements, but not potential job cuts.

Possible personnel reductions are not part of the consultation process at this stage, as we do not yet know how the operational changes will affect the number of personnel, said Nokia spokesman Doug Dawson.

But Antti Rinne, chairman of white-collar union Ammattiliitto Pro, said Nokia should discuss job cuts as well.

If an employer plans to change organization, the possible job cuts must be processed at the same time, according to the law, he said.

(Reporting by Terhi Kinnunen, Jussi Rosendahl and Tarmo Virki; Editing by Erica Billingham)