In theory, the U.S. Preventive Services Task Force has great clout in deciding which treatments and services private health plans must provide to their customers without imposing copayments.

Sen. Tom Harkin, an Iowa Democrat, included a provision in the 2010 health care law requiring private plans to cover procedures that get A and B grades from the task force. In practice, though, there have been some bumps in implementation, according to a federal panel of volunteer medical specialists convened by the Agency for Healthcare Research and Quality.

“It’s not just automatic that they say, ‘This is covered,’ and then you will never see a copay for it again,” said Karen Pollitz, senior fellow at the Kaiser Family Foundation.

She is an author of a 2012 report that found people sometimes were asked to pay for some costs associated with colorectal cancer screening, despite the service having an A recommendation from the task force.

The Obama administration issued guidance this month on how insurance plans must respond to the task force’s 2009 A recommendation on providing smokers and other users of tobacco with interventions to help them quit. In 2012, the nonprofit Campaign for Tobacco-Free Kids found that only four of the 39 health plans it analyzed clearly covered a full range of evidence-based tobacco cessation services, such as prescription and over-the-counter drugs as well as individual, group and phone counseling. In some cases, plans were requiring that patients pay part of the costs.

About 50 services now qualify for automatic coverage due to having top grades from the task force.

The task force was created in 1984. Its findings aided in setting insurance companies’ policies before the enactment of the 2010 health care law, said Clare Krusing, a spokeswoman for America’s Health Insurance Plans.

There have been complaints that the Harkin provision allows the task force to, in effect, “tap the bank,” said Mark V. Pauly, a professor of health care management at the University of Pennsylvania’s Wharton School.

In many cases, though, the task force recommendations may only serve to reinforce policies already in place at many insurance companies, “It’s kind of mopping up the stragglers,” Pauly said. “Of course, who knows what the future will bring? What if they invent some really great preventive service that costs $10,000 a year? But for the moment, it’s not a big deal.”