IntercontinentalExchange Inc. on Thursday urged CBOT Holdings Inc. shareholders and members to reject the proposed sale of the company to Chicago Mercantile Exchange Holdings Inc.

Energy exchange ICE, which has been pursuing the parent of the Chicago Board of Trade, told CBOT shareholders and members in a letter that the CBOT board has endorsed a deal with CME that undervalued the CBOT from the outset.

ICE Chief Executive Officer Jeffrey Sprecher said in the letter that CBOT's board has agreed to a bargain-basement sale in a transaction that would leave $1.3 billion of shareholders' money on the table, and urged them to vote against the deal.

At current share values, ICE said its financially and strategically superior offer for CBOT is worth $11.9 billion, while the CME deal is worth $10.6 billion.

The letter also said a merger between CBOT and Atlanta-based ICE would not create technological integration problems.

CBOT executives have said a merger with ICE would be catastrophic because of differences in technologies used.

ICE and CME, the largest U.S. futures exchange, have been locked in a bidding war for CBOT, the No. 2 U.S. futures exchange, since March.

CME recently sweetened the terms of its deal with CBOT, following an improved proposal from ICE.

ICE's sweetened offer came after the U.S. Department of Justice gave CME and CBOT regulatory clearance to merge.

CBOT members and shareholders and CME shareholders will vote on July 9 on whether to approve the merger.

(Reporting by Anupreeta Das)