Bain spent $80,000 during the fourth quarter to hire lobbyists from Public Strategies Washington Inc. to "monitor tax reform developments," lobbying records show. Joseph O'Neill and Paul Snyder are lobbying for Romney's former company.

O'Neill was chief of staff to former Senate Finance Committee Chairman Lloyd Bentsen and helped run the late Texas Democrat's 1988 vice presidential bid. Snyder was a legislative assistant to former House Speaker Tip O'Neill, the late Massachusetts Democrat.

Budget Deficit

Raising taxes on carried interest compensation wouldn't do much to narrow the U.S. budget deficit. In its fiscal 2012 budget request, the Obama administration said the proposal to tax carried interest as ordinary income would generate $14.8 billion over 10 years. In December, the deficit stood at almost $1.3 trillion.

The issue has divided Congress along mostly partisan lines. The last time the Senate considered a bill that would have increased taxes on carried interest -- in June 2010 -- every Republican voted against it, preventing the bill from advancing. Senator Ben Nelson of Nebraska was the only Democrat to oppose the legislation.

Few Defections

The same bill was passed in the House that year with 15 lawmakers in each party voting against their leaders.

As the debate over carried-interest taxation advanced in Congress, the Private Equity Growth Capital Council was formed in February 2007 so the industry could make its case more directly to lawmakers.

The group, whose members include the Carlyle Group LP, based in Washington, and New York-based Blackstone spent about $2.5 million that year lobbying Congress on issues that included measures to tax carried interest at the same rate as ordinary income. It spent $2.2 million on lobbying in 2011.

"We believe that tax policy should incentivize the kind of entrepreneurial risk-taking that private-equity firms take every day," said Ken Spain, a spokesman for the Private Equity Growth Capital Council, a trade group based in Washington. "We remain vigilant in respect to this issue. Private equity as an asset class is going to be a topic of discussion throughout 2012."

Spain is a former communications director for the National Republican Congressional Committee.

Comprehensive Overhaul

While the issue will be a central one in the presidential campaign and on Capitol Hill, the taxation of carried interest probably won't change until Congress considers a comprehensive tax-code overhaul. That would be difficult to enact before 2013.

One potential challenge for private equity is something that otherwise would be seen as a favorable development for the industry: a Romney administration. Ending the preferential treatment of capital gains if Romney wins the presidency could dissolve notions that he is a captive to his former industry, said Martin Sullivan, a contributing editor at Tax Analysts, a nonprofit organization in Falls Church, Virginia.