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 CornynMcConnell names Senate GOP tax conferees Air Force makes criminal reporting changes after Texas massacre We need a better pathway for allowing civilians to move guns across state lines MORE (Texas), Orrin HatchOrrin Grant HatchMcConnell names Senate GOP tax conferees Ryan pledges 'entitlement reform' in 2018 Utah governor calls Bannon a 'bigot' after attacks on Romney MORE (Utah), Mike LeeMichael (Mike) Shumway LeeSupreme Court takes on same-sex wedding cake case House approves motion to go to tax conference — with drama Trump really will shrink government, starting with national monuments 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.