With all the numbers being thrown around I found this to be informative -

Of 163.9 million households 87.8 million or 53.6% pay Income Tax

Of the non paying households 76.1 million or 46.4% pay no Income tax
But 28.3/46.4% pay payroll taxes
10.3/46.4% are elderly
Income under 20K 6.9/46.4%, non elderly income under 20K - should they have payroll taxes?
Others .9/46.4%

Of the 38 Million household who had no tax liability they took these credits

Elderly tax benefits - 16.7 Mil
Child, working poor - 11.6 mil
cash gifts - 2.3 mil
tax exempt interest- 1.9 mil
Itemized deducts - 1.9 Mil
Other credits - 1.0 mil
Capital Gains - .6 mil

An additional 38 million had no income tax liability because of a low income

So it appears that it's more like 77% who could be on the hook with 23% not -