(Bloomberg News) A majority of U.S. voters consider Barack Obama's health-care law to be a tax increase, leaving the president to defend an election-year vow not to raise levies on the middle class, according to a Quinnipiac University poll.

By a margin of 55 percent to 36 percent, respondents said the Patient Protection and Affordable Care Act amounts to a tax increase. Participants were less sure of what they thought about the future of the law, saying 48 percent to 45 percent that the U.S. Supreme Court was right to uphold it, while also saying 49 percent to 43 percent that Congress should repeal it.

Voters' view of the law as a tax might pose a problem for Obama as he takes on former Massachusetts Governor Mitt Romney in the November presidential election, said Peter Brown, assistant director of the Hamden, Connecticut-based Quinnipiac University Polling Institute.

"Obama has worked mightily to avoid the 'T' word," Brown said in an e-mailed statement accompanying the poll, conducted July 1-8. The main question is whether Republicans can convince voters that the health-care law "breaks his promise not to raise taxes on those who make less than $250,000," Brown said.

Results released from the same poll yesterday found Obama leading Romney, the presumptive Republican nominee, 46 percent to 43 percent, helped by a 2-1 advantage among single women.

Vote to Repeal

Romney and his fellow Republicans have been hammering Obama on the tax issue since the Supreme Court ruling last month. Yesterday, the Republican-controlled House voted once again to repeal the health-care law; the Senate has no plans to take up the measure and Obama has vowed to veto it.

Most respondents in the poll said the Supreme Court decision won't affect their vote; 27 percent said it would make them less likely to vote for Obama and 12 percent said it would make them more likely to support the president. Overall, 55 percent of voters said a candidate's position on health-care policy is either extremely or very important to them.

Americans are split, 48 percent to 47 percent, on whether everyone should have to carry health insurance, the poll found. Women support the mandate 50 percent to 45 percent; men oppose it by the same margin.

Obama's latest move on immigration fares better with voters, who approve 55 percent to 39 percent of his decision to stop the deportation of some young illegal immigrants.

Arizona Crackdown

Even so, voters say 61 percent to 34 percent that they want a law in their state similar to one in Arizona that would require police to check the immigration status of someone they have stopped or arrested if they suspect the person is an illegal immigrant. Obama's administration challenged that law, and the Supreme Court struck down much of it in June.

The House's vote to hold Attorney General Eric Holder in contempt because of his refusal to turn over some documents related to the Fast and Furious gun operation drew support from a subset of voters in the poll, 44 percent to 29 percent. A subset asked a different question said 42 percent to 36 percent that the vote was political rather than legitimate.

The survey of 2,722 registered voters has a margin of error of plus or minus 1.9 percentage points.