While many are crediting Obamacare as the biggest tax increase in U.S. history, it only ranks 10th in tax increases since 1950. Interesting that Reagan has 5 of the top 15.

http://www.motherjones.com/kevin-drum/2012/07/no-obamacare-not-biggest-tax-increase-historyThere have been 15 tax increases of significant size since 1950, and Jerry Tempalski, a tax analyst in the Treasury Department, has estimated the size of all of them as a percentage of GDP. Tempalski hasn't estimated the eventual size of ACA, but PolitiFact took a crack at it using the same methodology, and they figure that ACA amounts to a tax increase of 0.49% of GDP seven years from now. That places it tenth on the list.
It's fair for Republicans to complain that ACA includes a bunch of new taxes. It does. Most of them fall on high earners and corporations, not the middle class, but they're still taxes. However, the "biggest tax increase in history" nonsense is crazy, and no news outlet interested in accuracy should let it pass without challenge.