The Club for Growth political action committee has made what it calls a "substantial" TV ad buy in Indiana.
"If you live in Indiana, you will see this ad," says Club For Growth PAC spokesman Barney Keller.
The ad will run on both broadcast and cable outlets in the Hoosier State.
Keller would not disclose the amount of the buy from the political arm of fiscally conservative advocacy group.
The Howry Politics blog puts the number at $1.8 million.The ad asks Hoosiers to call Lugar's Senate offices about his record which includes votes for increased taxes on gasoline and social security and against spending cuts.
The ad buy helps cut into Lugar's big cash advantage in this suddenly hotly contested primary battle against State Treasurer Richard Mourdock.
In the most recent quarterly filing on December 31st, 2011; the Lugar campaign reported $4 million cash on-hand.
By contrast, The Mourdock campaign had just a little over $360,000.
The most recent polls on this race suggest Lugar's lead over Mourdock is down to a single-digit margin with the primary set for May 8th.