Iain McKenzie today slammed Atos Healthcare, which the UK Government uses to do the tests under a contract worth £100 million a year of taxpayers' money.
Mr McKenzie said he had seen first hand the 'disgraceful way in which people can be treated'.
He said: "A constituent who suffers from severe cerebral palsy and who could not travel was refused a home visit and told they had to go to Glasgow to be tested for work.
"Another constituent of mine who was seriously injured in an accident at work was advised to attend an Atos assessment in Glasgow, but again they couldn't travel because they were in so much pain.
"In addition, the constituent then had their benefit stopped because Atos sent the assessment forms to the wrong address."
Another Greenock man who is currently being helped by the MP told the Tele about his problems with Atos.
The former soldier, who did not want his full name published, suffers from dysthymia, a chronic form of depression.
He said: "The problem started 20 years ago when I was in the Army. I also suffer from irritable bowel syndrome, and both conditions make it very difficult for me to travel. But Atos wanted me to go to Glasgow for assessment over incapacity benefit.
"I asked to be tested at their Greenock office but there has been a lot of confusion over exactly where it will be done, and this is causing me a great deal of worry." Mr McKenzie believes the situation with the health assessments is leaving vulnerable people in dire straits.
He said: "I'm shocked and saddened that thousands of sick and disabled people up and down the country are experiencing immense hardship after being deprived of benefits following Atos's deeply flawed work assessment.
"The so-called work capability assessments are certainly not fit for purpose, and the test has left the most vulnerable people in our community in the most appalling of situations."