METRO passengers on Tyneside face travel problems this weekend as industrial action threatens to disrupt timetables.
Metro operator Nexus said it had pulled out of a deal to give staff a reduced working week after union leaders gave notice that members would walk out.
If agreement is not reached in the next few days, union members will stop work for 24 hours from 7pm on Sunday.
The strike threat is the latest in a long-running dispute between Nexus and the RMT and Amicus unions.
All sides thought they had reached an agreement last month when an 11th-hour deal was brokered at the conciliation service Acas.
Representatives of all sides provisionally approved reducing the average working week from 37 hours to 36, but members rejected the deal, insisting Nexus meet demands for a 35-hour-week.
Davey Hall, Amicus regional secretary, said: "We are still open to an invitation from the company to discuss this with them.
"Nexus is saying if industrial action is not withdrawn then discussions will not take place. The reality is, industrial action will not be withdrawn."
Nexus said yesterday that the unions were aware a 35-hour-week was only possible if it was "self-financing" - at no additional cost to the company or to passengers.
Nexus was told on Friday by RMT and Amicus that strike action was planned.
The operator said it had made repeated requests to the unions for an explanation for the industrial action.
Late on Friday, Nexus director general Mike Parker wrote to union officials and the chairman of their negotiating committee formally withdrawing the 36-hour-week offer.
Ken Mackay, director of Metro, said: "Our staff must be extremely confused. They are being directed by union officials to go out on strike and give up their pay for a reason which so far has not actually been communicated to management.
"I publicly invite their representatives to meet us in an attempt to start a positive dialogue, but there is no way that this can happen when the gun of industrial action is being held at our heads."
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