The IRS needs more cash from Congress to implement the new Republican tax code overhaul, the agency’s public advocate said Wednesday.

A new report from National Taxpayer Advocate Nina Olson to lawmakers highlights the need for more funding for the IRS to update tax systems, train employees, draft and publish new tax forms, answer calls from confused taxpayers and more. The cash-strapped agency hasn’t yet determined how much money it will need to implement the new tax law, but a preliminary assessment last year put the additional cost at roughly $495 million over fiscal 2018 and fiscal 2019, which begins Oct. 1.

“The IRS will have its hands full in implementing the new law,” Olson said. “We have already seen confusion about withholding changes, confusion about the deductibility of prepaid property taxes, and confusion about whether states can allow taxpayers to make charitable contributions in lieu of taxes” after Congress curtailed deductions for state and local property, income and sales taxes.

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The tax-collecting agency has faced deep spending cuts for years, including a 75 percent reduction in its employee training budget since fiscal 2009, according to the report. Congress provided $11.2 billion for the IRS in fiscal 2017, and the agency is now operating at the same funding level because lawmakers have yet to agree on new appropriations for fiscal 2018.

Implementing the most significant tax code changes in decades with tight resources will be no small feat.

For example, the GOP tax bill lowered a cap on the mortgage interest deduction from $1 million to $750,000, for debt incurred after Dec. 15, 2017, with certain exceptions. But the IRS doesn’t currently have detailed information about taxpayers’ mortgages, like the date of closing or terms of refinancing.

The agency “will have to develop clear guidance for taxpayers and develop forms and systems capacity to distinguish between loans subject to the $1,000,000 cap and loans subject to the $750,000 cap,” Olson said.

Another key challenge will be customer service, an area the IRS has struggled with for years, as lawmakers are quick to point out.

The IRS receives more than 95 million phone calls each year; during the upcoming filing season, they expected to answer about six out of 10 calls from taxpayers. And that projection was made before lawmakers rewrote the tax code in December.

The number of calls is likely to spike, if prior tax law changes are any indication, the report says. After Congress passed economic stimulus legislation in 2008, the IRS was “deluged” with more than 150 million telephone calls from taxpayers, a 125 percent increase from the previous year, according to the report.

While GOP appropriators in Congress have been eager to slash spending at the IRS in recent years, Treasury Secretary Steven Mnuchin has said he’s concerned about the lack of staff and resources at the tax-collecting agency.

Top lawmakers and the White House are now negotiating new topline spending levels for the current fiscal year and beyond, though progress has been slow. If a deal is reached on overall spending, it would likely be followed by a final appropriations package for fiscal 2018.