Italian Foreign Minister Franco Frattini told two newspapers Germany was trying to divide Europe by putting its national interests first.
"I will not accept competition based around national interests," Frattini told the Corriere della Sera and La Repubblica.
His German counterpart, Joschka Fischer, however, said Italy should be vying for a seat itself, rather than opposing Germany's bid.
"It would be loyal competition between countries that are friends and allies," Fischer said.
The Security Council is restructuring to give wider representation, and Germany is rallying for support. Brazil, India and Japan are also campaigning for a seat.
Germany's bid is not without critics at home, including former chancellor Helmut Schmidt, who said it was "not in Germany's interest to be involved in major decisions concerning war and peace and having to take responsibility for those decisions."