Government changes to the benefits system are already having a devastating effect on people with mental health problems, campaigners have said.
The group, including charity Mind, strongly criticised the work capability assessment (WCA), which will be used to reassess people on incapacity benefit.
In a letter to the Guardian, they said the changes were causing "huge" distress and had resulted in suicides.
Ministers said the test was being kept under regular review by specialists.
The government is seeking to reassess all 2.6 million people on incapacity benefit - and its successor employment support allowance (ESA) - by 2014 in an effort to encourage more people back to work and to cut the welfare bill.
The WCA determines whether applicants are entitled to the highest rate of ESA - for those deemed unable to work at all due to sickness or disability - or are considered "fit for work", in which case they are put on jobseeker's allowance instead.
The test, first introduced by the last Labour government and being rolled out by the coalition, can also place applicants into a "work-related activity group", where they will be expected to take steps to prepare themselves for work in the medium to long term.
Expressing their concerns about the process, the group of organisations wrote: "We've found that the prospect of IB [incapacity benefit] reassessment is causing huge amounts of distress, and tragically there have already been cases where people have taken their own life following problems with changes to their benefits.
"We are hugely worried that the benefits system is heading in a direction which will put people with mental health problems under even more pressure and scrutiny, at a time when they are already being hit in other areas such as cuts to services."
They added: "There needs to be a shift towards a more sympathetic and supportive system that genuinely takes into account the additional challenges people with mental health problems face and can make a real objective assessment of their needs rather than placing them into a situation where their wellbeing is put at risk."
The signatories include Mind chief executive Paul Farmer, Rethink boss Paul Jenkins, Centre for Mental Health joint chief executive Professor Bob Grove, Dr Jed Boardman of the Royal College of Psychiatrists, chief executive Bill Walden-Jones of Welsh charity Hafal, and Scottish Association for Mental Health chief executive Billy Watson.
Last month, six charities - including the MS Society and Parkinson's UK - said the assessments were declaring sick people fit for work, and called for changes to the system.
And earlier this year a group of cancer charities voiced their concerns in an open letter, also published in the Guardian, to Work and Pensions Secretary Iain Duncan Smith.
The Department for Work and Pensions (DWP) said it had accepted all the recommendations of an independent review of WCA by Prof Malcolm Harrington, completed in November.
He concluded that the test was not working as well as it should be and changes were needed to make it "fairer and more effective".
The WCAs are conducted by the DWP's independent medical adviser, Atos Healthcare, at more than 140 medical examination centres across the country.
The DWP said they were working closely with mental health campaigners to address their concerns and that all claimants had a right to appeal if they were unhappy with the outcome of their test.
A DWP spokeswoman said: "We have already put in place his [Prof Harrington's] recommendation to create a network of 'mental health, intellectual and cognitive champions' in each Atos Medical Examination Centre to spread best practice and build understanding of these conditions.
"In consultation with charities such as Mind, Prof Harrington is now looking at the way mental health is assessed in the WCA and we look forward to receiving his recommendations later this year."