In his column in the Mail on Sunday he said that business secretary Vince Cable had “given the game away” by saying the tax would hit homes valued as low as £1m.
Johnson said: “This tax is not only brutally unfair on people who happen to be living in family homes, but it would hit the economics of new housing developments.
“It is time people woke up to the horror of what is being planned. Labour and the Lib Dems currently claim that this tax would fall only on homes that are valued above £2m.
“But everyone knows these thresholds have a habit of falling.”
It was estimated that a £1m property could be taxed by £10,000 per year.
Johnson added: “It is hard to think of a tax that is more viciously unfair. It hits families who have worked hard and traded up the property ladder only to find themselves walloped for their success.
“Above all, a tax on these higher value homes would not only clobber existing owners, it would make it more difficult to build the new properties I have described and that we so desperately need.”