Boris Johnson has been described as "out of touch" with Wales after saying there were too many places in the UK where English wasn't the first language.
Mr Johnson said he wants everyone who moves to Britain "to be and to feel British ... and to learn English. That's the most important thing." He said there were "too many" parts of Britain where English is not people's first language "and that needs to change".
But his words, which were part of a speech at a Tory leadership hustings in Darlington on Friday, were criticised in Wales.
Plaid Cymru MP Jonathan Edwards said: "The crass, dog-whistle, anti-immigrant sentiment of Mr Johnson’s comments is only matched by its stupidity. It just proves that Wales isn’t even an afterthought to him.
"Today’s latest gaffe only reaffirms the fact that this leadership contest is one of the best adverts for Welsh independence imaginable."
Welsh Liberal Democrats leader Jane Dodds, who is hoping to win the Brecon and Radnorshire by-election from the Tories, said: "Here in Wales we know that not speaking English as your first language is no barrier to having a thriving community.
"Boris’ crass comments show just how out of touch he is with areas like ours in Wales where people can freely and proudly speak Welsh as part of their daily lives."
But not everyone reacted the same way, saying Mr Johnson's comments were clearly directed to inner-city areas with high levels of immigration rather than Wales as a whole.
David Owens, from Cardiff , said: "It's obvious to me that he is referring to people coming into the UK. He is talking about cities like London and Birmingham where there are high levels of immigration and where immigrants might not be fully integrated into British society."
For others it was more about national identity. "Boris Bach, wake up the UK is not England, Britain is not England, but Wales is Welsh," said one on social media.
