As a partial government shutdown approaches its two-week point, concerns are growing that a heavily impacted Internal Revenue Service will delay issuing taxpayers' refunds.

The agency has categorized issuing tax refunds as a "non-excepted" activity — meaning those tasked with processing refunds would be furloughed during a shutdown. Meanwhile, several types of tax return processing were deemed "Necessary for the Safety of Human Life or Protection of Government Property."

That's according to a December shutdown plan that lays out the first five business days of the agency's response during a shutdown occurring outside of tax season. While the document notes the plan can be reassessed and furloughed employees can be recalled, The Wall Street Journal reported Wednesday and CNN reported Thursday that the IRS generally does not issue refunds during a shutdown.

The IRS plan says that only 12.5 percent of the IRS workforce is authorized to work during a shutdown, while the rest of the agency faces furloughs.

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That plan might be revised as soon as Friday, as the agency shifts into tax season, which typically starts in mid-January, CNN reports, citing a source familiar with the matter.

As budget negotiations to reopen the government have stalled over President Donald Trump's demand for funding to build a border wall, the risk is growing that tax refunds could be delayed if furloughed IRS workers don't return to work.

H&R Block Senior Tax Analyst Jon Helpling says that taxpayers shouldn't wait for a shutdown resolution before filing their taxes, even if the potential for a lengthy tax refund delay exists.

A delay in tax refunds is likely to disproportionately affect low-income Americans, The Wall Street Journal reports. With little or no income-tax liability, these taxpayers often use a sizable refund to help pay down debt, the publication says.

Contributing: Justin L. Mack, Indianapolis Star; The Associated Press.