A tax on sales of high-dollar real estate in Boston would generate an enormous amount of money for affordable housing, but could dampen the city’s real estate market and faces a long road to approval.

That’s what emerged from a City Council hearing Tuesday on a proposal that would levy a 6 percent tax on most homes, land, and office buildings that sell for more than $2 million, with the proceeds going to the city’s affordable housing fund.

A tax of that size would have generated $420 million last year, according to data from City Councilor Lydia Edwards, one of the bill’s cosponsors. Even a tax on commercial and industrial properties alone would have generated $189 million, nearly quadrupling the city’s current affordable housing budget of roughly $50 million.