CyberSource Corp., the online payment provider that Visa Inc. is buying, is being sued by a pension fund that contends the $2 billion takeover will shortchange investors.

CyberSource directors are obliged to get the highest price for the stock, lawyers for the Inter-Local Pension Fund of the Graphic Communications Conference of the International Brotherhood of Teamsters said in a lawsuit filed Tuesday.

Visa's bid "undervalues the company's true worth," according to the complaint in Delaware Chancery Court. "There is no indication" that directors "took reasonable steps to obtain the best value."

Visa said in April it would buy CyberSource in Mountain View, Calif., for $26 a share, a 34% premium at the time.

A Visa spokesman declined to commen. A CyberSource spokesman did not reply to inquiries.