If President Obama endorses any level of cuts to Medicare or Medicaid, his grassroots support will take a major hit, according to one liberal group organizing an "Obama donor strike."

The warning from liberal activists comes a day before the president is set to deliver a major speech on the nation's debt and is expected to call for reducing Medicare and Medicaid costs.

The Progressive Change Campaign Committee (PCCC) seized on that Tuesday afternoon and said that within just two hours of an email appeal to Obama backers, some 40,000 of them had already signed an online petition promising to withhold financial support from his reelection campaign. Should Obama endorse the idea of cutting either program, the group says backers are pledging to not donate to or volunteer on next year's campaign.

"Many people still want to believe in President Obama," an email sent from the group earlier Tuesday read. "But the White House needs to understand that their actions now will have real consequences for 2012. The level of grassroots enthusiasm will be determined by whether the President fights for bold progressive change — and takes cuts that hurt grandparents, the disabled, and kids firmly off the table." 

The group plans to deliver the signatures of their online petition to Obama's 2012 campaign headquarters in Chicago and is highlighting comments from former donors and volunteers. 

"Like many volunteers on his campaign, I was in love with the idea of Obama," wrote Susan Carpenter, identified as an Obama volunteer from Ohio. "I haven't given up on him quite yet, but I'm mustering the energy to work on the resistance. He needs to know who we are." 

The PCCC has proven to be one of the loudest voices on the left criticizing Obama over the past year. During last year's lame-duck session, it funded TV spots slamming the president for an agreement with Senate Republicans to extend Bush-era tax cuts.