Around 2.4 million poor families face an average hike in their council tax bills of £138 next week, according to an anti-poverty charity.
Research for the Joseph Rowntree Foundation (JRF) found that abolishing council tax benefit will leave 150,000 families paying an average £300 more a year while 1.9 million claimants that do not pay anything now will be billed an average £140 per year.
The benefit is being replaced by a new system, council tax support, that will be run by English local authorities but on 10% less funding. Pensioners are protected under the reforms, leaving working-age claimants to bear the brunt of the cuts, according to JRF.
Chris Goulden, head of poverty at JRF, said: "Some of the country's poorest families must find £140 extra from their strained household budgets to pay council tax for the first time. Making up the shortfall will be beyond most, with working hours under pressure and benefits falling behind inflation. This tax hike will push people into poverty or cause more hardship for already very poor households, taking money from families who had little to start with."
In the report, written by the New Policy Institute (NPI) for JRF, around 300,000 claimants living just above the breadline were found to be at risk of falling into hardship.
It found 232 local authorities have devised schemes that will demand council tax from everyone regardless of income while 58 will retain current levels of support for families.
Sabrina Bushe, researcher at NPI, said: "From Monday over two million households that were previously deemed too poor to pay council tax will find hefty bills landing on their doormats. Hitting only the poorest and most vulnerable, this tax increase - which won't raise much more money than it costs - is both unjust and unwise."
A spokeswoman for the Department for Communities and Local Government said: "Council tax benefit spending doubled under Labour and welfare reform is a vital part of help to tackle the deficit that we inherited. The localisation of council tax benefit will give councils stronger incentives to cut fraud, promote local enterprise and get people back into work.
"Council schemes should have taken into account the impact on vulnerable people. For people facing genuine hardship, there are free advice services who can offer help and support, and many councils have put in place hardship funds to provide financial assistance to people in difficult circumstances.
"In contrast to when council tax doubled under Labour, this Government has taken action to freeze council tax bills for three years. As a result council tax has fallen by just under 10% in real-terms, helping hard-working families and pensioners by providing much-needed cost of living assistance."