Senator Bernie Sanders of Vermont, a potential Democratic presidential candidate known for far-left stances on issues of economic inequality, introduced legislation on Thursday that would increase the number of wealthy Americans subject to the estate tax.

With the bill, Mr. Sanders joins a growing chorus of left-wing politicians calling for new ways to tax the rich. Last week, Elizabeth Warren, the Massachusetts senator who has announced her 2020 candidacy, introduced a plan for a so-called ultramillionaire tax on households with a net worth of $50 million or more. And Representative Alexandria Ocasio-Cortez of New York recently proposed a 70 percent top rate on income over $10 million a year, intensifying the conversation within the Democratic Party about tax policies aimed at addressing income inequality.

In his plan, Mr. Sanders proposed applying an estate tax when someone leaves assets worth more than $3.5 million to his or her heirs, the same level as in 2009. The plan significantly lowers the threshold under the current tax law, passed in late 2017, which raised the amount an individual is allowed to transfer before facing any estate tax to roughly $11 million; couples can pass on twice that much.

The tax-the-rich proposals, including the one introduced by Mr. Sanders, are designed to increase revenue to pay for expanded social programs like “Medicare for all.”