Britain's largest labour union has also scheduled 24-hour stoppages on Aug. 6 and 20 and a 12-hour strike on Aug. 13 at the Alwyn, Elgin and Dunbar platforms in the North Sea if it is unable to agree new rotas with Total.

No formal talks with Total were planned but some informal contact is ongoing, he said.

Separately, GMB union said on Tuesday that its members working on Equinor's Mariner platform had received a pay offer from their employer oil services firm Aker Solutions to avoid strike action. The offer is the same as for those represented by Unite the Union.

GMB said workers were being consulted on the pay deal. On Monday, Unite said workers would be balloted Aker's offer.

The two unions had previously voted in favour of industrial action.

A spokesman for Unite said that a third ballot for strike action for workers at the Offshore Contractors Association had not yet gone out. This ballot would be sent to 2,500 workers in oil services in the British North Sea.

(Reporting by Shadia Nasralla and Julia Payne, editing by Louise Heavens and Alexandra Hudson)