Ken Livingstone has accused mayoral rival of "calling Londoners workshy" after Boris Johnson urged workers in the capital to look to foreign staff for tips on getting jobs.
Speaking to the Sun, Johnson said: "Look at Pret a Manger. If you've been to one recently, how many native Londoners served you? What's going on?
"London is a fantastic creator of jobs — but many of these jobs are going to people who don't originate in this country.
"They are hard-working, good people, and we need to learn from them and understand what it is that they have got that makes them able to get those jobs that young Londoners don't have."
Livingstone, who surged ahead of Johnson in a shock poll on Thursday, said the mayor was "out of touch with reality."
"Boris Johnson has two jobs, earning him £400,000 a year combined, so it is little wonder that he is so out of touch about how hard it is for many to find work in a city with some of the highest unemployment in Britain.
"The Tory mayor seems oblivious to the real problems young Londoners face. He should be working round the clock to create new jobs for Londoners, but instead he has been silent as his Conservative government has cut EMA and raised tuition fees."
Following the poll Johnson said May's mayoral election would be a "tough fight."
"Times have been tough, the economy has been tough. But I want to bring forward a fantastic manifesto for taking the city forwards."