Instead, Isberg wrote, enacting the 4.2 percent rate retroactively during 2012 would be easier to implement, because many payroll systems self-correct when tax rates change.
Fiorille, of Rochester, New York-based Paychex, said the $18,350 cap would create a new wrinkle that would cause difficulty and extra work during the payroll industry's busy season.
"We'll do it," he said. "We always get it done."
Intuit Inc., which makes QuickBooks accounting software for small businesses, would be able to update its system quickly once it receives the necessary information from the Internal Revenue Service, Sharna Brockett, a public relations manager for the company, said in an e-mailed statement.
"Regardless of the outcome, any changes should have minimal effect on our customers and their ability to process payroll with the latest tax rate," Brockett said.
Smaller Businesses
Smaller businesses that use off-the-shelf software or prepare pay stubs by hand would also face difficulty complying with late changes.
"It's a complication in the employer's life and I think the smaller employers are the ones who are going to feel the confusion more directly," said Abe Schneier, a senior technical manager at the American Institute of Certified Public Accountants in Washington.
People who work for themselves and pay both the employer and employee sides of the tax will have trouble ensuring they make the correct quarterly estimated tax payments, he said.
Schneier said he thought that large payroll providers would face complications, though would largely be able to manage the changes.