Republican presidential candidate Newt Gingrich is hunkering down in the trenches of the Southern battleground for Super Tuesday with a robocall attacking Rick Santorum for being a "big labor conservative."

This is the first paid advertisement against Santorum from the Gingrich campaign. The call is set to begin Friday in Oklahoma and Tennessee and will reach 150,000 households in each state.

The robocall, narrated by a woman, was recorded Thursday. The ad begins by saying Santorum "talks a good game" about his blue collar roots, and that he doesn't want you to know Santorum "cozied up to the labor union bosses" and voted against a national right-to-work bill that would have let workers opt out of paying union dues. "Union dues that hurt families and small businesses. Rick Santorum, friend of working families or the union bosses pal? You decide."

Since venturing to Tennessee and Georgia for a week of campaigning, Gingrich has attacked Santorum in speeches at various campaign stops. On Thursday he urged voters not to vote for "Pennsylvania big labor baloney." Gingrich's daughter Jackie and former presidential candidate Herman Cain will travel to Tennessee next Tuesday. Later in the week Jackie, Cain and J.C. Watts will travel to Oklahoma to campaign for Gingrich.