Besides lacking coverage information that would help the agency enforce the “individual mandate,” the IRS also is hamstrung in penalizing those who do not sign up. The lawmakers who drafted the health-care law intentionally barred the IRS from using its customary tools for collecting penalties — liens, foreclosures and criminal prosecution. The only means of collecting the fine is to essentially garnish tax refunds for people who overpaid their taxes.

Enforcing compliance with the law is just part of what one Treasury Department official calls “the largest expansion of IRS responsibilities in recent history.” And the increased workload comes as the IRS is suffering from high turnover of senior managers, years of budget cuts and congressional inquiries into the alleged politicization of the agency.

“This is really quite a heavy lift,” former IRS commissioner Mark W. Everson, who served under President George W. Bush, said in recent testimony on Capitol Hill, adding that he was concerned about the agency’s ability to fulfill the wide-ranging demands of the Affordable Care Act…

Some of the tasks are so vital to the success of President Obama’s health-care initiative that any uncertainty about whether the IRS can do its job raises doubts about the overall endeavor. Health-policy researchers say they know relatively little about what level of enforcement is necessary to nudge citizens into buying coverage or whether the health law’s low fees — $95 in 2014 or 1 percent of income, whichever is greater — will succeed in doing so.