Labour policies are turning the party's natural supporters away from it "almost daily", the leader of Britain's largest private sector union has said.
Derek Simpson said skilled employment was "haemorrhaging"
Amicus general secretary Derek Simpson said its third term could be its last.
It was "sickening" ministers had attacked last month's pensions strike by council workers, Mr Simpson added.
And it may be too late to turn round policy enough "to avoid meltdown at the next election and the nightmare of a Tory government", he said.
Mr Simpson told his union's journal that progress in implementing measures agreed with ministers before the last general election had, after a sluggish start, now "dried up" altogether.
"The haemorrhage of skilled, well-paid jobs in manufacturing and the finance sector has continued apace.
"Shockingly, job cuts now even hang over the heads of our members in the NHS."
Mr Simpson added: "To make matters worse, the government seems determined to accommodate business attempts to casualise the labour market.
During the past six months the "perpetrators of the great pensions robbery" had "gone unmolested as they condemn millions of people to poverty in retirement", he said.
"A long list of companies like Rentokil, Arcadia and Harrods have all closed well-funded schemes and replaced them with nothing worthy of the name of pension.
"The government has not even lifted a finger to address this issue."
Ministers had continued to turn against "working people and their trade unions", Mr Simpson added.
"Even the simplest promise made to working people before the election is to be watered down.
"The promise bank holidays will no longer be included in the calculation of the statutory four weeks' paid holiday is to be phased in over a period of years and the benefit will be taken into account in the calculation of future rises in the minimum wage."