By Michael Hernandez

WASHINGTON

 The Senate Banking Committee voted 18-4 Thursday to approve a controversial bill to increase sanctions on Iran.

Six Democrats joined 12 Republicans to support the bill, with all four votes against coming from Democrats.

The bill’s supporters have said it is necessary to keep pressure on Iran while negotiations over its nuclear program continue.

“It is clear that further action is necessary to compel Iran to reach an acceptable agreement,” committee chairman Sen. Richard Shelby said in a statement.

Democrat Sen. Robert Menendez and Republican Sen. Robert Kirk co-sponsored the bill. But Menendez and nine other Republicans agreed to hold off on a full vote on the measure, which is almost certain to pass, until a key March 24 deadline is reached in international negotiations on Iran’s nuclear program.

The senators said in a letter to President Barack Obama that while they remain skeptical that Iran is committed to making the concessions world powers seek, “We remain hopeful that diplomacy will succeed in reversing Iran’s ability to develop a nuclear weapon capability.”

Democrats' support is critical as lawmakers would need two-thirds support from both houses of Congress in order to override a veto on the bill, which Obama has promised. Republicans currently hold 54 seats in the 100-member Senate, requiring at least 13 additional votes from their Democrat counterparts to make the bill veto-proof.

The March 24 deadline for a political framework agreement will be followed by a June 30 deadline for a comprehensive deal. The legislation would impose additional sanctions should negotiators fail to reach a deal by the end of June.

The sanctions that were eased during negotiations would go back into effect after July 6, and would be implemented in waves. 

Negotiators from the U.S., Britain, China, France, Russia, Germany and Iran have been attempting to broke a deal with the Islamic Republic for 18 months in order to bring its nuclear program under international monitoring and ensure the country does not get a nuclear weapon. Two previous deadlines have passed without the hallmark comprehensive accord.