Kirk, a five-term congressman, accused Democrat Alexi Giannoulias on Monday of engaging in the "reckless lending that brought our U.S. economy to its knees."
The bank Giannoulias' family owns is trying to shore up its shaky finances. Broadway Bank entered into a consent decree with regulators in late January that gives it 90 days to raise money, deal with troubled assets and improve management.
Kirk says Giannoulias must answer questions about his involvement with bad loans at the bank.
Giannoulias worked at the bank before being elected state treasurer in 2006.