The Pattali Makkal Katchi PMK), which is reportedly opposed to English names for Tamil films, has demanded that the actor-director change the name of the film that is being made in Hindi and Tamil.
Kamal Haasan, speaking at a British Deputy High Commission-sponsored discussion on freedom of expression and responsibility, said: "My film will remain 'Mumbai Express'."
"It is only a small political group," he said.
"If I mend my ways, it will not do good to society," the veteran actor said.
"They think but for the word 'Mumbai' there is a lot of English in the rest of the name."
"The Tirunelveli Express is still called by the same name. I think they should take their cultural revolution to the railways," he said.
"Too many times they (political pressure groups) have taken away boxes of films from theatre houses." It was time to stop this, he said.
This is the third Kamal Haasan film that has got into a row over its name.
His film "Sandiyar" had to be renamed "Veerumandi" because of objections from political groups.
Doctors' groups had objected to the name of his film "Vasoolraja M.B.B.S.".