The White House budget would increase Internal Revenue Service spending by 18 percent, providing a significant boost for an agency that has seen its funding levels decline by more than 10 percent since 2010.

President Obama’s proposal calls for $12.9 billion for the IRS in fiscal 2016, compared to the $10.9 billion that Congress appropriated for the agency through fiscal 2015. It would provide more than $650 million for tax-enforcement activities and invest additional money in new digital services such as an online tax-filing status and online payment options.

IRS Commissioner John Koskinen warned agency employees this month that he may need to shut down the organization for a few days this summer because of budget constraints, saying the spending package that Congress and Obama agreed to for fiscal 2015 may not be enough to make it through the year. The legislation reduced the IRS appropriations by $346 million compared to fiscal 2014.

The IRS claims to bring in $6 for every $1 of investment, due to its function as a tax-enforcement organization. But the agency has increasingly done more with less in recent years, despite taking on new responsibilities under the Affordable Care Act, also known as Obamacare.

Aside from its shrinking budget, the IRS workforce has also dwindled, decreasing by about 15 percent since 2009.

The result has been lower performance, according to Congress’s nonpartisan Government Accountability Office, which said in a report this year that the IRS budget and staffing cuts have “adversely affected operations,” including with a near doubling of telephone wait times during the past four years.

National Taxpayers Advocate Nina Olson said in a report this month that U.S. taxpayers will face the worst levels of IRS service in more than a decade during the upcoming filing season, with as few as 43 percent of callers reaching an agent.