A group of Republican senators are set to unveil a long-awaited constitutional amendment to require a yearly balanced budget.

The sweeping legislation, which calls for an annual spending cap and a legally mandated balanced budget, with some exceptions, will be unveiled Thursday by five GOP senators: Jon Kyl (Ariz.), John CornynJohn CornynImmigration battlefield widens for Trump, GOP Congressional investigations — not just special counsels — strengthen our democracy Wrath of right falls on Google MORE (Texas), Orrin HatchOrrin HatchHatch urged Trump to ‘speak clearly’ against hate groups The Memo: Trump tries to quiet race storm Senators push FTC to finalize changes to contact lens rule MORE (Utah), Mike LeeMike LeeTrouble draining the swamp? Try returning power to the states Congress must act to protect data privacy before courts make surveillance even easier Five tough decisions for the GOP on healthcare MORE (Utah) and Pat Toomey (Pa.). The proposed amendment goes beyond requiring a simple balanced budget each year, and seeks to enact a series of other fiscal reforms. 

Under the proposal, the president would be forced to submit a balanced budget to Congress each year. But Congress would also face certain constraints in its work to pass the budget.

The amendment would mandate that total outlays each year could not exceed total receipts by the government, unless both the House and Senate agree to an excess in outlays by a two-thirds vote. Any tax increase would also be required to pass both houses with the same two-thirds supermajority.

The Republican proposal would also cap spending each fiscal year at 18 percent of gross domestic product, a provision that could be waived by Congress during a time of war, or by a three-fifths majority of the House and Senate in a time of other military conflict.

Both the House and Senate would also be forced to cobble together three-fifths majorities to authorize an increase in the debt ceiling, according to the GOP measure.

The reforms would, if enacted, make it much tougher to authorize new spending.

The GOP amendment would need to be approved by a two-thirds majority in the House and Senate, a tough climb especially because Democrats control the Senate. Even if lawmakers somehow managed to advance the amendment, three-fourths of the states would still have to ratify it for the amendment to become part of the Constitution.