Dr David Mackereth has worked for 26 years as an NHS doctor but was told he could not be employed as a Department for Work and Pensions (DWP) disability assessor if he refused to identify patients as being of a sex that they did not see themselves as.
The 55-year-old father of four believes sex is genetic and biological, so established at birth.
He now claims his right to freedom of speech has been denied and he has been classed "unfit" to work for the department because of his religious convictions.
And, the medic from Dudley in the West Midlands fears many other professional people of faith could also be dismissed simply for holding opinions about gender that are "centuries old".
Dr Mackereth, who registered as a doctor in 1989 and spent most of his career working in Accident & Emergency wards, said: "I'm not attacking the transgender movement. But, I'm defending my right to freedom of speech, and freedom of belief.