Tory chairman Brandon Lewis has asked Boris Johnson to apologise for his remarks about people wearing burkas.
The ex-foreign secretary was accused of Islamophobia after writing in his newspaper column that Muslim women wearing them “look like letter boxes”.
He rejected a ban on full-face veils but said they looked “ridiculous”.
He was criticised by Labour MPs, some Tories and Muslim groups, who said the party was not doing enough to tackle prejudice.
Earlier, Foreign Office Minister Alistair Burt said there was a “degree of offence” in Mr Johnson’s comments.
Mr Lewis said he agreed with Mr Burt and called on the MP and former London mayor to apologise.