The Fire Brigades Union has written to the chairman of the National Joint Council - the fire service's forum for employees and employers - asking it to acknowledge that the Mer-seyside fire authority is wrong.
The union has given the NJC until August 3 to respond, or a meeting will be convened in Liverpool to call for national industrial action in support of Merseyside firefighters.
The dispute, which has resulted in two eight-day strikes involving 1,400 firefighters, centres on the fire authority's plans to promote non-uniformed staff to management positions.
The fire authority said it has conceded to the union's calls to block civilian staff from promotion in this way, but the union feared they would go ahead with the plans regardless.
The fire authority's stance is that the plan would encourage more women and ethnic minority applicants to the fire service, but the FBU disagrees.
The Fire Brigades Union's general secretary, Andy Gilchrist, said yesterday that the national executive was not going to leave the Merseyside members alone in the struggle.
"They have resolved that I shall write to the chair of the national employers on the National Joint Council seeking assurances that the Merseyside fire authority shall be dealt with and that the national machinery in place is upheld by them," he said.
"In the absence of any assurances being given I shall call for national industrial action in support of our Merseyside members."
The firefighters in Merseyside first went on strike for eight days earlier this month. During the action, which ended on Saturday morning, the army's green goddesses received 2,223 calls and the vehicles attended 720 incidents.
The cost of emergency cover has reached £1.6m and will rise unless a solution can be found to end the second strike, which began on Monday.
Tony McGuirk, the deputy fire chief, said it had been a local issue from the start and it should not be a national issue. He said he did not think it should compromise the safety cover of the whole of the UK.
He said he understood the frustration and anger among the firefighters over the impasse.
Merseyside's chief fire officer Malcolm Saunders has refused to speculate on how the fire authority would recoup the cost of the dispute.
