Mr Cameron is expected to use a speech later to call on the public sector unions to halt planned industrial action and accept that their pension packages must be reformed.
He will say the public sector must accept that the current pension arrangements are “not fair to the taxpayer” and unsustainable.
The Prime Minister’s comments could fuel the fire of public sector discontent. Already up to 750,000 public sector workers – including teachers, lecturers and civil servants – are planning a mass walkout on Thursday this week.
The National Union of Teachers (NUT) estimates that up to 85 per cent of schools will be at least partly shut.