On the recordApril 15, 1997
Revenue increases subject to the supermajority requirement include: Income taxes, and I think we all know what a direct income tax is; estate and gift taxes; employment taxes, including Social Security and Medicare; and excise taxes, such as Superfund, aviation, gasoline. Things that would not be included under the amendment would be tariffs, user fees, voluntary Medicare premiums, the Part B premium, and bills that do not change the Internal Revenue laws even if they have revenue implications. On the question of de minimis, de minimis is one-tenth of 1 percent, which, under the current Tax Code, would be about $300 million a year.
Source
govinfo.gov
