Boris Johnson has condemned proposals for a tax raid on owners of expensive homes, insisting the focus should be on ensuring firms like Google pay their way.
The Mayor of London, in a speech to the CBI , warned that high rates of personal taxation will make Britain less competitive.
Mr Johnson hailed the economic success of the capital but stressed that it could not be taken for granted.
"In the 19th century London became the biggest and richest city on earth because of its openness to trade and to talent," he said.
"I am worried that we are losing some of that openness at a critical time."
Mr Johnson called for a new "Age of Enterprise", saying it requires the Government to be "responsive to what is happening in the rest of the world".
"I am afraid that high rates of personal taxation are likely to make us less competitive," he said.
"We should have taxes that are low but fair and it is absurd to be suddenly whacking up taxes on cash poor people who happen to inhabit expensive houses in London when firms like Google are paying zero.
"Neither arrangement strikes me as being fair and so Google and co face a very clear choice - they can either change their tax arrangements or do much more to serve our society by visibly taking on 18 to 24-year-olds who are out of work."
His intervention came after Business Secretary Vince Cable indicated some kind of levy on property is being considered for inclusion in next month's Autumn Statement.
The Lib Dems have been pushing for a new wealth tax and there have been reports council tax bands could be hiked for properties worth £1m.
This is despite both David Cameron and George Osborne insisting the Government would not introduce a so-called "mansion tax".
The Chancellor is negotiating on the contents of his key statement on December 5, which is set to include a fresh round of welfare cuts.
Mr Cable said on Sunday: "These areas are under discussion and the devil will be in the detail but it is right that we do tax wealth and property is the obvious place to go.
"One reason that it is fairer is that it cannot run off to Monaco and Liechtenstein. When trying to deal with abuse of the tax system, it is the best way of doing it."
In his CBI speech, Mr Johnson also urged politicians to be positive about the country's prospects and stop using the "rhetoric of austerity"
"If you endlessly tell business to tighten their belts and eat nut cutlets and drink their own urine then you will be putting a big downer on growth and enterprise," he declared.
"Give British firms the right platform for enterprise and there are no limits to what they can achieve."
He insisted it was time to stop "vilifying bankers" but said leading bankers must now show "moral leadership" to help Britain's recovery.