HELSINKI, March 8 (Reuters) - Finland's prime minister said on Friday he had failed to persuade trade unions to call off planned strike action triggered by the government's labour market reforms, extending an ongoing conflict.

The standoff began last year when the newly elected right-wing government announced plans to favour local work agreements over centralised bargains, limit political strikes, cut social welfare and make it easier to terminate work contracts.

Industrial, logistics and electrical workers will on Monday begin a two-week strike targeting exports, imports and cargo transportation, the latest in a series of trade union actions in protest at the government's plans.

Prime Minister Petteri Orpo said on Friday he had urged union bosses to call off the strike because of its cost to companies.

"It will have a negative impact on the already struggling Finnish economy and employment," he said, adding that the strikes would not sway government opinion.

Companies like refiner Neste, steel maker SSAB and paper producer UPM have said they expect significant impact on their business from the planned strike.

The unions have said they are most upset by the fact the government no longer wants to include them in negotiations over labour market reforms, and are ready for a long fight if needed.

The government and business lobbies say Finland needs to boost productivity and cut its fiscal deficit to fight an ongoing recession and maintain the country's public welfare system for the longer term. (Reporting by Essi Lehto, editing by Terje Solsvik and Christina Fincher)