The rare sight of some 20,000 off-duty police officers marching through London will be particularly embarrassing for Cameron, whose centre-right Conservatives pride themselves on being the party of law and order.
"Prime minister, actions speak louder than words," the Police Federation union said in full-page adverts published in several national newspapers on Thursday.
"Police officers feel strongly that the government cutting the police budget by 20 per cent, privatizing core policing roles and pushing ahead with its ill-considered police reforms could jeopardize public safety," the union said.
The Conservatives and their junior Liberal Democrat partners have vowed to press ahead with unpopular austerity plans despite both parties suffering badly in local council elections last week amid discontent that the country had fallen back into recession after two years of deep spending cuts.
Public hostility to austerity has hit governments across the European Union, with French President Nicolas Sarkozy ousted by Socialist Francois Hollande who promised a gentler approach on debt reduction, and Greece in political crisis after voters deserted the main parties.
"(Finance Minister) George Osborne's austerity plans are beginning to sicken everyone," said Gail Cartmail, assistant general secretary of Britain's largest union, Unite.
Nick Herbert, the minister in charge of policing, defended the government's actions.
"It's very important that tough decisions are taken to deal with the deficit and the police service, police officers, I'm afraid, can't be exempted from that. I really don't think that would be fair," Herbert told Sky News.
Police officers have been legally barred from taking industrial action since the 1990s.
The Police Federation, which represents 135,000 low-ranking officers in England and Wales, said Thursday's action could be larger than the biggest police protest staged in Britain, in 2008, over a pay row with the then Labour government.
"We're at the lowest ebb I can ever remember," Paul McKeever, the federation's chairman, told Reuters.
Cuts to police budgets and a government-commissioned report that recommended allowing officers to be sacked, pay cuts for some and raising the pension age, have all caused disquiet.
"We're not against change," McKeever said. "What we're against is ill-informed change based on ideology which is going to damage the service, damage officers and, most importantly, damage the public as well."
On Wednesday, the government announced it was pressing ahead with proposals to overhaul public sector pensions. Those plans prompted one of the most widespread strikes ever seen in Britain last year.
Thursday's strike will include teachers, health-care workers and lecturers as well as members of the Public and Commercial Services (PCS) union which represents the likes of tax officials and immigration staff at airports.
BAA, the owner of London's Heathrow, Europe's busiest airport, said it did not envisage significant disruption but said there might be some delays.
"It is very disappointing that a minority of unions insist on carrying on with futile and disruptive strike action which will benefit no one," said Cabinet Office Minister Francis Maude. "Pension talks will not be reopened and members are risking losing a day's pay for nothing."
Thursday's protest is unlikely to be the end of the action. Len McCluskey, Unite's general secretary, has already warned that public spending cuts justified action during London's Olympic Games which start in July.
A spokesman for the PCS union said: "We are already talking about the possibility of further action in June. We haven't got any plans to (strike during Olympics). What we're focusing on is co-ordinating national action with other unions."