Mike Jackson, Unison’s senior national officer, said there would be an ‘explosion of anger’ because nurses and NHS staff are losing money due to the high cost of fuel.
Unions say the current allowance does not cover the soaring cost of fuel because it has not been significantly improved since the year 2000, although there was a small interim increase at the beginning of the year.
A crunch meeting of union representatives and employers this week will decide whether the allowance can be increased.
A review of the allowance should have been completed in time for the meeting this week – but looks unlikely to be concluded in time.
Unions have already asked for an immediate 5p per mile increase on all vehicles.
Mr Jackson said trusts will face dire consequences unless the allowance is improved.
He said: ‘In our view this review is not going to be completed on time. I think there will be all sorts of protests around this.
‘Staff are not going to put up with a situation where they are subsidising their employer by using their cars to work.
‘We have told staff to hold off until this meeting – but there will be an explosion of anger if we don’t settle this matter.’