( CNN ) -- Elizabeth Warren , the White House consumer-protection adviser now running for a U.S. Senate seat from Massachusetts , ripped into the tax plan put out by Mitt Romney , the state 's former governor , at the Democratic National Convention on Wednesday night . `` He wants to give tax cuts to millionaires and billionaires , '' said Warren , a former Harvard law professor who served as the Senate watchdog over the 2008 bank bailout . `` But for middle-class families who are hanging on by their fingernails ? His plans will hammer them with a new tax hike of up to $ 2,000 . '' That 's a lot of money to average folks , so let 's take a closer look . The facts : . Warren 's figure is drawn from the verdict of the nonpartisan Tax Policy Center , a joint project of the Brookings Institution and the Urban Institute that reviewed the Republican presidential nominee 's proposals . An August 1 analysis by the nonpartisan group cautions that it 's not a precise scoring , since Romney has n't provided enough specifics . But it found that under what Romney has said he wants to do `` would provide large tax cuts to high-income households , and increase the tax burdens on middle- and/or lower-income taxpayers . '' `` This is true even when we bias our assumptions about which and whose tax expenditures are reduced to make the resulting tax system as progressive as possible , '' the center noted . Romney wants to cut today 's income-tax rates , which date back to the Bush administration 's tax cuts of 2001 and 2003 , by 20 % and eliminate the alternative minimum tax on high earners . Romney says he will make up the lost revenue in part by limiting deductions , exemptions and credits currently available to top-level income earners , though wo n't say which tax breaks he plans to eliminate . CNN Fact Check : About those 4.5 million jobs ... If a Romney administration got rid of tax breaks like deductions for mortgage interest , health insurance and charitable contributions for top earners and cut them only by 42 % for households that earn less than $ 200,000 , the lower-income families with children `` would pay , on average , $ 2,000 more in taxes , '' the group concluded . Households without children would see a $ 75 cut under that scenario , the group stated . The study was written by Samuel Brown , a former Federal Reserve analyst ; Adam Looney , who served on the Obama administration 's Council of Economic Advisers ; and William Gale , who served on the same advisory board during George H.W . Bush 's presidency . President Barack Obama 's campaign seized on the $ 2,000 figure , using it in campaign ads targeting voters in swing states like Ohio , Florida and New Hampshire . The Romney campaign disputed the findings of the study when it was released , arguing that the analysis was flawed because it did not account for Romney 's promise to keep the share of taxes paid by top earners the same and that a reduction in the corporate tax rate -- another part of Romney 's plan -- would lead to more revenue . `` There 's an old expression in the computer world : garbage in , garbage out , '' Romney told Fortune magazine in an August 15 interview . `` They made garbage assumptions and they reached a garbage conclusion . '' The study 's authors said it worked under the assumption that any reductions in revenue due to the corporate rate cut would be made up elsewhere . Conclusion : . The $ 2000 `` tax hike '' figure that Warren cites is grounded in a third-party analysis that Romney has criticized , but one the authors stand by . The authors also note that their calculations are not precise because they lack some specifics of Romney 's plan . CNN 's Matt Smith and Lindsey Knight contributed to this report .
Democrats say Romney tax plan will cost middle-class families $ 2,000 . The figure comes from a study from the Tax Policy Center , a nonpartisan think-tank . Romney called it a `` garbage conclusion , '' but the authors stand by their findings .