US stock exchanges Nasdaq OMX and IntercontinentalExchange have stepped up calls for a merger with NYSE Euronext, urging NYSE shareholders to push for meetings between the three boards.
NYSE Euronext, which has twice rejected an offer from Nasdaq-ICE in favour of an earlier agreement for a friendly acquisition by Germany's Deutsche Boerse, is "rushing" shareholders into a vote to distract them from regulatory obstacles facing the Deutsche Boerse deal, Nasdaq-ICE said in a letter.
ICE and Nasdaq made an $11.5bn (£7bn) unsolicited offer for NYSE Euronext on April 1 – a deal valued at about $1bn more than Deutsche Boerse's offer.
But NYSE has refused to meet, saying it sees too many risks in such a combination and the merger would not meet its strategic objectives.
Nasdaq-ICE are now taking their case to shareholders directly, and have said they will make a hostile tender offer later this month.
NYSE shareholders are set to vote on the Deutsche Boerse deal on July 7.
"Don't let them railroad you into the clearly inferior Deutsche Boerse transaction without all the information you need in order to make an informed decision as the ultimate owners of NYSE Euronext," the letter said.
"Demand of your board that they meet with us, and at the same time ask them, 'What's the rush?'"
The NYSE and Deutsche Boerse combination faces what are expected to be steep hurdles for regulatory approval in Europe, because together they would control virtually all futures trading from London to Frankfurt.
NYSE management has said it does not expect to have approvals by the July 7 vote.
Nasdaq and ICE have repeatedly said their combination is more likely to get regulatory approval – although critics say their dominant market share in U.S. stock-listings would likely raise U.S. antitrust concerns.