The former Archdeacon of Wells is campaigning for a change in the way people with mental health problems are assessed for employment and support allowance.
The Venerable Dick Acworth said people with mental health problems were at a disadvantage in the Work Capability Assessment, which judges whether they are fit for work.
Mr Acworth's son has bipolar disorder but was deemed to be fit for work by the Department for Work and Pensions (DWP). Mr Acworth appealed the decision and when the judge read evidence from his son's psychiatrist, the DWP's judgement was thrown out.
Now Mr Acworth has launched a campaign against the "unfair" Work Capability Assessment said: "People with mental health problems are substantially disadvantaged by how they are being assessed and many are found fit to work when they are very unwell."
A petition launched by the Archdeacon is asking Secretary of State for Work and Pensions, Iain Duncan Smith, to temporarily stop reassessing people with a mental illness who are being moved from incapacity benefit to the new Employment and Support Allowance, until changes are made to the test to ensure it is fair.
Mr Acworth's position reflects that of three judges, who in May ruled as part of an ongoing judicial review of the assessment, that the process was unfair for people with a mental illness and puts them at a "substantial disadvantage".
He added: "If my son didn't have parents to support him, I don't know what he would have done. I really fear for other people who don't have anyone to help them through such a difficult process."