Union leaders fear taxpayers' cash will be used to bail out a rail company at the centre of a bitter safety dispute.
Train users using Sunderland, Seaham, Hartlepool, Seaton Carew and Durham stations have endured reduced Northern services on 16 consecutive Saturdays.
The dispute, between the operator's owners, Arriva Rail North, and the Rail Maritime and Transport (RMT) workers' union, is set to continue for the three remaining Saturdays this month.
Now the RMT is calling for Transport for the North, a partnership of local transport operators, transport authorities and businesses, to intervene at its Thursday morning by publicly backing the union's case.
The RMT wants guarantees fears the introduction of new trains will be used as an excuse to jeopardise the future role of guards.
It is also urging Transport for the North to oppose any Government plans to use tax payers' money to bailout Arriva Rail North for lost revenue during the lengthy dispute.
In the letter to TfN board members, general secretary Mick Cash warns that: "Arriva Rail North have no incentive to resolve the dispute because the Government will reimburse the company for revenues lost as a result of the industrial action.
"Parliamentary questions have shown that the Government is considering a request from Arriva Rail North to be reimbursed.
"The Rail Minister has said the terms of this bailout is 'commercially confidential' although we do believe that the company will have already been issued a “letter of comfort” from the Government.”
"I would now urge all Transport for the North members to show some independence from Whitehall, and issue a clear unequivocal statement that you expect Arriva Rail North to keep a safety critical guard on all trains and that the government should refuse to bailout Arriva Rail North for revenues they have lost as a result of industrial action.
"All RMT is asking for is that Northern passengers keep a safety critical guard on every train and that passengers will continue to benefit from the safety and operational competencies guards currently provide."
Arriva Rail North, which insists guards will be guaranteed employment until the end of Northern's franchise in 2025, ran eight trains in either direction along the Newcastle-Middlesbrough line with this Saturday's emergency timetable still to be confirmed.