Among those lobbying wavering Republican lawmakers to support "Plan B" is Sen. Rob Portman (R-Ohio), who said he and other unnamed GOP senators were "asked to make some calls."

But Portman took his lobbying efforts a step further by visiting the House floor to lobby conservative Republicans. He said he spoke with members from his home state of Ohio "and other midwestern states."

Asked if he supports Plan B, Portman said he did: "I support it as a step to get a broader agreement"on avoiding the fiscal cliff.