Four out of five civil servants are prepared to strike if the Government does not back down and lift the cap on public sector pay, a ballot has revealed.
Members of the Public and Commercial Services union (PCS) overwhelmingly backed industrial action, increasing pressure on ministers to end the controversial policy of holding down the pay of millions of workers.
There was a 49% turnout in the consultative ballot of around 150,000 civil servants, the highest in the union's history.
The PCS will now move to a formal strike ballot and is expected to push for co-ordinated industrial action with other unions in the new year.
The union will now demand urgent talks with the Government in the run-up to this month's Budget and seek discussions with MPs to ensure the Chancellor awards an above inflation pay rise to all public sector workers.
PCS general secretary Mark Serwotka said: "This is an incredible result and a damning indictment of government pay policy.
"Members have sent a clear signal that the cap must go and that they are prepared to fight for a decent pay rise.
"Prime Minister Theresa May and Chancellor Philip Hammond have a clear choice, they can take note of this vote of their own staff and take action now or ignore it at their peril.
"Weasel words about waiting for pay review bodies in the spring won't cut it. Our members are part of the 55% of the public sector that are not covered by these bodies.
"We need action now from the Government, not a promise of jam tomorrow."
The union represents staff in Government departments, jobcentres, courts, border posts as well as other employees including driving test examiners.