They are lobbying Boris Johnson to make what they call "fat-ism" illegal and a punishable offence on the same level as racism, ageism and gender and religious discrimination.
Bettina Bender, employment law partner at CM Murray, said: "Most people would agree that no one should be verbally or physically abused because of how they look. But from an employment law perspective granting employees special protection on the grounds of their size would seem a protection too far."
It is currently unlawful for employers to discriminate against employees or workers on the grounds of sex, pregnancy, marital status, race, nationality, ethnic origin, age, disability, sexual orientation, gender reassignment, religion or belief .
And Bender thinks adding a new protected group on the basis of their size would raise issues such as how overweight an employee needs to be before they qualify for protection.
She added: "What happens if [an overweight claimant] has lost weight before they get to tribunal and if they have brought a claim they may in fact stoke further ridicule.
"The reasons for being overweight can be complex and the diet industry feeds off people's insecurity regarding weight. Education from an early age on healthy eating and access to medical advice and support seems to be a more sensible approach to the issue of weight."
