David Cameron has been accused by campaigners of breaking the law by cracking an "appalling" joke comparing Commons Speaker John Bercow to one of the Seven Dwarfs.
A charity which helps people with primordial dwarfism and other forms of restricted growth said the comments were a form of harassment - and called for talks with the Prime Minister.
In a dig at Mr Bercow - believed to be 5ft 6in tall - Mr Cameron said health minister Simon Burns had asked his driver to reverse into the Speaker's car.
When Mr Bercow said he was "not happy" about the incident, Mr Cameron quipped to journalists at a Westminster lunch on Wednesday, Mr Burns retorted: "So which one are you?".
In June, Mr Burns publicly apologised after calling the Speaker a "stupid, sanctimonious dwarf" in the Commons.
He said he was sorry for any offence he had caused after the insult was branded "derogatory and deeply offensive" by the Walking with Giants Foundation (WWGF).
Mr Cameron's spokeswoman said he had made "light-hearted comments not intended to cause offence".
But John Connerty, WWGF co-founder and charity secretary, launched a fierce condemnation of the Prime Minister's decision to "glorify" the previous incident.
"Once again we have an influential figure, if not the most influential person in the country, making distasteful references about a person's lack of height," he said.
"It was bad enough having a minister of health make similar distasteful comments but to have the Prime Minister himself glorify the comments in a joke is totally unacceptable and downright appalling."