OSLO, May 15 (Reuters) - Wage talks between Norwegian oil service firms and two labour unions broke down on Wednesday and will later switch to state-led mediation in an attempt to prevent strike action by workers, the unions and companies said.

The Industri Energi and Safe unions had been negotiating since Tuesday with Offshore Norway, which represents companies, such as Schlumberger, Subsea 7 and Baker Hughes.

If Norway's government-appointed mediator is unable to broker a deal, up to 6,000 union members will be eligible to go on strike, affecting oil and gas drilling services, maintenance and the installation of new equipment.

Strikes among oil service workers tend to have limited impact on petroleum output in the short term, but may cause delay to projects in case of prolonged conflict.

The Norwegian oil and gas companies that operate offshore fields, including state-controlled Equinor, agreed a wage deal with their workers earlier this month, preventing strike action. (Reporting by Nerijus Adomaitis, editing by Terje Solsvik)