Most uninsured people in the U.S. have yet to try to sign up for health coverage under Obamacare, and a key advocacy group said it will hire more workers to reach those unfamiliar with the law.

About 68 percent of uninsured Americans haven't yet used online marketplaces run by the federal government or states to sign up for a health plan, according to a survey released today by Enroll America, a nonprofit group with ties to the White House that is promoting the law in 11 states. Many people without insurance think they can't afford coverage and don't know federal subsidies under the 2010 Patient Protection and Affordable Care Act can help pay their premiums, the group said.

Enroll America said it would increase its field staff by 30 percent, or 58 people, to educate uninsured people about the financial assistance available under the law.

“One of the biggest barriers, bigger than any technical problem, is people believe they won’t be able to get affordable insurance,” Tresa Undem, a pollster who conducted Enroll America’s survey, said on a conference call for reporters. “That’s their history. That’s their experience; they say ’I can’t afford health insurance.’”

About 2.1 million people selected private health plans under the Affordable Care Act in time to have coverage starting Jan. 1, the first date it was available, according to the U.S. Department of Health and Human Services. Enrollment for 2014 coverage under the law, known as Obamacare, ends on March 31. The Obama administration estimated that 7 million people would use the new exchanges to gain coverage in 2014.