Ahead of next month's rise in the hourly rate to £6.08 for adults and £4.98 for 18 to 20-year-olds, Unison said it feared attempts by business groups to prevent a rise next year would throw millions into poverty.
General secretary Dave Prentis said: "A freeze or cut in the minimum wage would not only hit poor families hard, it would be bad for business, as it will hit spending power and stunt growth and recovery."
He continued: "As inflation increases and the Government's cuts run deep, low paid workers are being driven into poverty. A small rise would be outstripped by the rising cost of essentials like food, fuel and transport. That is why Unison is calling for a substantial increase and a move towards a more realistic living wage of £8 an hour.
"Despite the claims of self-interested business lobbyists, there is no evidence that the minimum wage has caused unemployment in the last decade - it is the Government's economic strategy that is throwing people on to the dole."
Unison said there was a growing problem of some agencies in the home care sector "driving down" paid hours and not paying travelling time between home visits to the elderly and disabled.
"We desperately need an increase in the minimum wage rise to restore the balance of fairness and to help to stimulate growth across the economy," said Mr Prentis.
The adult minimum wage rate will increase by 15p to £6.08 an hour in October, the rate for 18 to 20-year-olds will increase by 6p to £4.98, for 16 to 17-year-olds it will go up by 4p to £3.68 and for apprentices it will increase by 10p to £2.60 an hour.