The Republican Party and GOP House and Senate members face a new threat if they go along with President Obama to back tax hikes to avert the "fiscal cliff" on January 1: Donors will abandon them.

Key conservatives have alerted Republican leaders that they will organize a campaign to steer donors away from those backing tax increases, a real threat that could starve the party of the money needed to boost its membership in the House and Senate in the 2014 elections.

"If the Republican Party breaks its word to the American people and goes along with President Obama with tax increases, it will have betrayed conservatives for the final time," warned Brent Bozell, head of the conservative group ForAmerica in a letter hand delivered to Republican National Committee Chairman Reince Priebus.

"I will make it my mission to ensure that every conservative donor to the Republican Party that I have worked with for the last three decades-- and there are many and they have given tens of millions to Republican causes--gives not one penny more to the Republican Party or any Member of Congress that votes for tax increases. The GOP will not deserve their support," added Bozell.

Bozell's group, which claims over 3.5 million supporters, is being backed by other anti-tax groups such as Americans for Tax Reform, headed by Grover Norquist.

"To see the Republican leadership in Congress and numerous other GOP representatives and senators, day after day, talking about breaking their promise to their constituencies to not raise taxes is appalling," wrote Bozell. "Indeed, if Republicans break their promise to the American people and vote for tax increases, the only thing going off the cliff will be the Grand Old Party itself."