In a note, the company said that service would be suspended between 6.30am - the usual time of opening - and 9.30am, and that trains are only likely to be circulating normally some half an hour afterwards.


To offset the impact of the strike, Lisbon bus operator Carris is to lay on extra services on routes that coincide with the metro lines, the statement said.


On Friday, an arbitration tribunal ruled that a skeleton service was only necessary for security and maintenance departments on Tuesday, not the actual running of trains.


The action is the fourth partial strike in the metro this year, as metro employees contest government moves to farm out the metro concession, as well as staff reductions. The call for public tender is open until 14 May.