"They're going to have to figure out who this applies to and how long it will last," said Neal Weber, a tax partner in the Washington office of Cherry Bekaert & Holland LLP. "Those are the major issues."

The earlier proposals wouldn't have allowed the deduction for income from banking, insurance, financing or investing. Professional sports teams, golf courses, country clubs, tanning facilities and adult-entertainment companies also wouldn't have been eligible to claim the deduction.

Kautter said there is concern that other small companies that earn large profits, such as law firms or dentists' offices, might benefit from the deduction.

Not 'Modest' Income

"It could clearly apply to businesses that earn a substantial amount of money," Kautter said. "There are a lot of law firms that are less than 500 employees and they're not known for their modest income."

Cantor has said the 500-employee standard comes from the U.S. Small Business Administration's definition of a small business. In a Feb. 19 Fox News interview, he rejected concerns that the deduction could benefit high earners.

"We are all in this together," he said. "We have got to as a country work towards growth in this economy."

The 2010 proposal would have allowed companies to claim the deduction for two years. Republicans may be more reluctant to support the break if it is viewed as another temporary measure that could spark a political fight when its expiration nears, said Evan Liddiard, a former senior tax policy adviser to Republican Senator Orrin Hatch of Utah. The party was bruised by fights in December and this month over extending a payroll tax cut for workers that was due to lapse.

Another Extender

"There would be some skepticism about a temporary deduction," said Liddiard, now a partner at Urban Swirski & Associates LLC, a Washington lobbying firm. "This would add another extender to the code."

Regardless of the path Cantor chooses, the deduction won't encourage small companies to significantly increase hiring or investment, said Mark Zandi, chief economist of Moody's Analytics Inc.