Governors in five states say they oppose expanding their Medicaid programs under President Barack Obama's health-care overhaul, and another 26 haven't decided, an option created by a U.S. Supreme Court ruling that may prevent millions of low-income Americans from obtaining insurance.

Governors of Florida, Louisiana, Iowa, South Carolina and Mississippi object, saying they're concerned rising health-care costs may force tax increases or cuts to services, even as the federal government is promising to cover all the added Medicaid costs in the first three years and 90 percent after that. The federal reimbursement is about 59 percent now, on average.

Most of the governors resisting the Medicaid expansion are Republicans who objected to the health-care law as unconstitutional or too costly. If all 31 states don't go along, as many as 11.4 million Americans who would otherwise be eligible for expanded Medicaid may be left without the coverage that Obama and Congress intended to offer, according to the Urban Institute, a Washington-based research group.