By JILL LAWLESSLONDON (AP) â¿¿ Government welfare reforms that include a contentious cut dubbed the "bedroom tax" will cause upheaval for some of Britain's most vulnerable people, religious leaders and anti-poverty activists claim. The measure, which takes effect Monday, will reduce rent subsidies to social housing tenants if they have a spare bedroom. The government â¿¿ which prefers the term "under-occupancy penalty" â¿¿ says it is one of a series of changes that will make the country's unwieldy welfare system simpler, cheaper and fairer. But thousands of trade unionists, advocates for the disabled and anti-poverty campaigners held protest marches against the change on Saturday, and on Sunday four churches released a joint criticism of the reforms. The Baptist Union of Great Britain, the Methodist and United Reform churches and the Church of Scotland argued that "the cuts are unjust and that the most vulnerable will pay a disproportionate price." "Our feeling is that these benefit changes are a symptom of an understanding of people in poverty in the United Kingdom that is just wrong," Methodist spokesman Paul Morrison told the BBC. "It is an understanding of people that they somehow deserve their poverty, that they are somehow 'lesser', that they are not valued." Archbishop of Canterbury Justin Welby, leader of the Anglican church, has also criticized the welfare reforms. The British government is trying to reduce public spending by 50 billion pounds ($76 billion) by 2015 in a bid to deflate Britain's ballooning deficit and kick-start its spluttering economy. It says its welfare reforms will save 4.5 billion pounds by 2014-15. The measures include changes to disability benefits, below-inflation increases and, eventually, the replacement of a patchwork of housing, unemployment and parental benefits with one payment called the Universal Credit. The Department for Work and Pensions says the spare-bedroom levy â¿¿ a cut of 14 percent to households with one extra room and 25 percent for two â¿¿ will save taxpayers money and will help free up social housing for families because people with too many rooms will downsize.