Hunter Howard Jr., president of the 2,200-member chamber, said the assessment cap would cause more problems than it would solve.
"It's not really a tax cap, it's a tax shift," Howard said. "About 20 percent of the taxpayers are going to get a benefit, but 80 percent of them are going to pay for that."
The study, which was conducted by Columbia-based Miley and Associates and commissioned by the chamber, looked at the impact of capping growth in property assessments statewide and in seven of the counties currently undergoing reassessment. In Beaufort County alone, 73 percent of taxpayers would pay more taxes if the cap were imposed than without the cap, the study found.
In June, the General Assembly passed a bill that would cap five-year increases in a property's assessed value at 20 percent in most cases. Gov. Mark Sanford still has not chosen whether to sign or veto the bill but said last week he would make a decision "shortly." Sanford also may take no action on the bill, in which case it becomes law in January.
The governor's spokesman, Will Folks, said Wednesday the report is "obviously something the governor is going to consider as he continues to look at this proposed legislation."
The study found that about 32,000 Beaufort County taxpayers would have higher property tax bills if there is no cap. But if the cap becomes law, more than 72,000 taxpayers would pay more in taxes.
If the cap is rejected, about 67,000 Beaufort County residents could have lower tax bills, the study found. But if the cap is enacted, only about 26,000 residents could have lower tax bills.
In addition, Beaufort county's tax rate would have to be almost double what it is now in order to maintain the approved level of spending, the study found.
County finance director Tom Henrikson did not return calls Wednesday but previously has said the county and all governments that receive funding through property taxes -- including schools, municipalities, fire districts and public service districts -- would have to increase their tax rates if the assessment cap becomes law. If the governments are limited in what they collect from the wealthy, they would have to increase the tax levy for all residents, he said.
Howard said enacting the assessment cap would be like opening a "Pandora's box" that the state cannot afford. If the bill becomes law, the chamber of commerce could file a lawsuit seeking to block the legislation from taking effect, he said.
"Number one, we're going to call on the governor to veto the legislation and encourage him to do so because of the precedent it sets ... and then secondly, depending on his response, we will be determining whether we go to the court or we go to the General Assembly as the next step," Howard said.
But Sen. Scott Richardson, who ushered the cap through the Senate in the final days of this year's legislative session, said the chamber was scared that caps on individuals' taxes would lead to higher taxes on businesses.
"The state chamber of commerce is not in the business of helping individual taxpayers, they're in the business of helping big companies in the state," said Richardson, R-Hilton Head Island. "They don't see it as lowering the tax burden, they see it as increasing the burden on corporations."
Richardson said he favored a more comprehensive overhaul of the state's tax code that would limit property and income taxes while increasing consumption taxes like that on gasoline, saying the existing tax code was outdated and needed to be modernized. At least offering the cap in property assessment would be an improvement, he said.
"What the legislature saw is that's about as fair a system as the legislature could come up with," Richardson said. "It would be predictable, you wouldn't be taxing people off their property. That's what we were trying to get at."
Howard said the chamber's motivation had nothing to do with corporations but everything to do with small businesses.
"What we are concerned about are the small businesses that are going to get hammered as a result of this legislation," Howard said. Along with lower-income homeowners, small businesses "are going to be one of the two primary entities subsidizing the wealthy."
The chamber's study comes after Clemson University's Strom Thurmond Institute released a study in March that also found that an assessment cap essentially would be a tax break for the wealthy while requiring a tax increase on the poor.
"With a reassessment cap, some property owners would subsidize the property taxes of others," that study found. If a cap is instituted, "many property owners will see a higher tax bill than they would have after conventional reassessment."