(AP) -- Budget cuts at the IRS could delay tax refunds, reduce taxpayer services and hurt enforcement efforts, IRS Commissioner John Koskinen said Thursday.

About half the people who call the IRS for assistance this filing season won't be able to get through to a person, Koskinen said. Once tax returns are filed, there will be fewer agents to audit them.

"Everybody's return will get processed," Koskinen told reporters. "But people have gotten very used to being able to file their return and quickly getting a refund. This year we may not have the resources, the people to provide refunds as quickly as we have in the past."

In recent years, the IRS says it was able to issue most tax refunds within 21 days, if the returns were filed electronically. Koskinen wouldn't estimate how long they might be delayed in the upcoming filing season, which is just a few weeks away.

Congress cut the IRS budget by $346 million for the budget year that ends in September 2015. The $10.9 billion budget is $1.2 billion less than the agency received in 2010.

The cuts come as the IRS is starting to play a bigger role in implementing President Barack Obama's health care law. For the first time, taxpayers will have to report on their tax returns whether they have health insurance.

Millions of taxpayers who are receiving tax credits to help pay insurance premiums will have to report them as well.

Some Republicans in Congress have vowed to cut IRS funding as a way to hurt implementation of the health care law. Koskinen has said it won't work.

He said the IRS is required to enforce the law, so other areas will have to be cut, including taxpayer services and enforcement.

Kosinen said the IRS is imposing a hiring freeze, except for emergencies, and is eliminating almost all overtime.

"In some ways, these budget cuts are really a tax cut for tax cheats," Koskinen said. "Because to the extent we have fewer people to audit and enforce the tax code, that means some people cutting corners on their taxes or not complying are going to get away with it, and that is a decision that Congress has made."

The National Treasury Employees Union represents IRS workers. Union President Colleen M. Kelley said waits at IRS walk-in centers will stretch for hours and "correspondence will continue to pile up and taxpayers will wait longer and longer for a response."

"Starving the IRS hurts more than just the agency's workforce, it hurts all taxpayers," Kelley said.

Koskinen called Thursday's news conference to highlight tips for choosing a qualified tax preparer. He said it is important to check preparers' qualifications and work history, confirm their fees and always review the tax return before signing it. He said taxpayers should be wary of preparers who promise big refunds.

The tax filing season generally starts in mid-January, though it has been delayed in recent years because of last-minute tax changes enacted by Congress.

Once again, Congress passed a tax bill this year just before going home for the holidays, extending more than 50 temporary tax breaks that had expired. Koskinen, however, said the filing season would start on time next month, though he said the agency was not yet ready to announce the exact date.

Each year, millions of taxpayers file their returns in the first few weeks of the filing season so they can get fast refunds. This year, refunds averaged about $2,800.

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Online: IRS tips for choosing a tax preparer: http://tinyurl.com/md38gqe

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