The Senate Budget Committee’s top Republican accused the White House of violating a bipartisan agreement on spending limits with its new budget, a sign of tough going for administration priorities.

In the first congressional hearing on President Obama’s budget plan, Alabama Sen. Jeff Sessions confronted White House budget director Sylvia Burwell about the president’s proposal to spend $28 billion on public works, education, job training and other “investments,” with another $28 billion earmarked for the Defense Department.

“You are spending over what the law requires,” Sessions said.

Obama’s budget request came in $56 billion above the $1.014 trillion limit on discretionary spending that was agreed to in a deal reached in December by Sen. Patty Murray, Democrat of Washington, and Republican Rep. Paul Ryan of Wisconsin. Burwell said spending would be paid for by raising taxes and tightening tax loopholes.

Both sides were anticipating an election-year clash over the budget as Obama pushes Democratic Party priorities and Republicans, mindful of their political base, seek to keep check on spending.

Obama’s $3.9 trillion budget proposal would benefit low-income families, college students, researchers and highway users. In turn, he’s is asking more from airline passengers, U.S. multinational companies and high earners who would pay a “fair share tax” to pick up the tab for the added spending.

It also emphasizes differences with congressional Republicans, who plan to offer a budget plan of their own.

Under questioning by Sessions, Burwell acknowledged that exceeding the so-called discretionary spending limit by $56 billion “will require an amending of the law.”

It wasn’t clear what lawmakers might do about the $56 billion, if anything.

Sen. Rob Portman, an Ohio Republican, said the White House didn’t do enough to rein in entitlement programs, such as Social Security or Medicare.

“These programs are not sustainable,” said Portman, who was director of the Office of Management and Budget under Republican President George W. Bush. He said Obama’s answer seemed to be “tax more and more.”