Elizabeth Warren will propose a minimum tax on the nation’s richest companies.

Senator Elizabeth Warren of Massachusetts and her allies will propose a minimum tax on the profits of the nation’s richest companies, regardless of what they say they owe the government, as part of Democrats’ $3.5 trillion economic and social-policy package.

Ms. Warren’s so-called “real corporate profits tax” was a key part of her presidential campaign, and she has enlisted Senator Angus King, the Maine independent, to help press her case that profitable companies should be taxed, regardless of loopholes and maneuvers that have allowed many of them to avoid federal corporate income taxes altogether.

The measure would require the most profitable companies to pay a 7 percent tax on the earnings they report to investors — known as their annual book value — above $100 million. By taxing the earnings reported to investors, not to the Internal Revenue Service, Democrats would be hitting earnings that companies like to maximize, not the earnings they try hard to diminish for tax purposes.

“During the presidential campaign, Joe Biden and I disagreed on some tax policies, but there was one thing we strongly agreed on: corporations shouldn’t be able to tell shareholders they were making huge profits, then tell the I.R.S. they made nothing in profits,” Ms. Warren said in an interview.