A ballot of civil service workers is likely to back significant changes in the sector's pension scheme.
Civil servants are likely to vote yes for the government's plan
Under the plans, new recruits will retire at 65, with their pension based on average earnings over their career rather than their final salary.
But, more than 600,000 existing members of the scheme can still retire at 60.
The two biggest unions - Prospect and the PCS - have recommended that members back the changes. The alterations were agreed after lengthy negotiations.
Voting for the union ballots closes later on Friday.
Question of age
The government originally proposed that all civil servants, who have a traditional final-salary pension scheme, should eventually have a retirement age of 65.
But, it backed down from this idea just before the last general election in the face of threatened industrial action by union members.
Union leaders are now happy with the changes, especially as existing civil servants who are in the scheme no longer face the possibility of working to 65.
"I have no hesitation in endorsing the recommendation for a 'yes' vote in the pensions ballot," said Prospect's general secretary Paul Noon, when the ballot started.
"Union negotiators have done an excellent job in securing a good deal for existing members as well as concluding the details of a good quality, indexed linked, defined benefit, whole career scheme for new entrants."
However, the government's eventual deal was criticised by Lord Turner, the chairman of its Pensions Commission.
In May, he said that keeping the civil service scheme in its present form for existing members was out of step with the government's plan to raise the state pension age to 68, in line with his own recommendations.
The new civil service scheme, to be called Nuvos, will come into effect for people who join from 1 August this year.
Its main features are:
- Staff contributions of 3.5% of salary
- A retirement age of 65
- A pension calculated on average career salary
- Faster build up of pensions - at a rate of 2.3% (1/43rd) of salary a year
- Continued inflation protection for pensions in payment
The changes to the civil service scheme are part of the government's plan to change most public service pension arrangements, including those for local government staff, NHS workers, teachers and firefighters.
The government wants to make sure that the cost of these schemes does not rise any further, partly because of the continued trend for people to live longer.