Iris I. Burnell, the manager of a Jackson Hewitt Tax Service office on Capitol Hill, said she met this week with a client in his late 50s who has several part-time jobs and wants to buy insurance on the exchanges. But, she said, “he’s finding that the costs are prohibitive on a monthly basis, so he has resigned himself to the fact that he will have to suffer the penalty.”

When Congress was writing the Affordable Care Act in 2009 and 2010, lawmakers tried to balance carrots and sticks: subsidies to induce people to buy insurance and tax penalties “to ensure compliance,” in the words of the Senate Finance Committee.

But the requirement for people to carry insurance is one of the most unpopular provisions of the health law, and the Obama administration has been cautious in enforcing it. The I.R.S. portrays the decision to go without insurance as a permissible option, not as a violation of federal law.

The law “requires you and each member of your family to have qualifying health care coverage (called minimum essential coverage), qualify for a coverage exemption, or make an individual shared responsibility payment when you file your federal income tax return,” the tax agency says on its website.

Some consumers who buy insurance on the exchanges still feel vulnerable. Deductibles are so high, they say, that the insurance seems useless. So some think that whether they send hundreds of dollars to the I.R.S. or thousands to an insurance company, they are essentially paying something for nothing.

Obama administration officials say that perception is wrong. Even people with high deductibles have protection against catastrophic costs, they say, and many insurance plans cover common health care services before consumers meet their deductibles. In addition, even when consumers pay most or all of a hospital bill, they often get the benefit of discounts negotiated by their insurers.

The health law authorized certain exemptions from the coverage requirement, and the Obama administration has expanded that list through rules and policy directives. More than 12 million taxpayers claimed one or more coverage exemptions last year because, for instance, they were homeless, had received a shut-off notice from a utility company or were experiencing other hardships.