Having been rebuffed once, Nasdaq OMX and IntercontinentalExchange have come out fighting in their bid to hijack Deutsche Boerse's planned takeover of Nyse Euronext, insisting that their proposal is "superior by a significant and inescapable margin".
Nyse Euronext and Deutsche Boerse agreed a tie-up worth around $9.7 billion in February, potentially creating the world's biggest exchange operator.
However, earlier this month Nasdaq OMX and ICE joined forces to launch a counteroffer for Nyse Euronext which they say is worth 21% - or $2 billion - more based on yesterday's closing prices.
This was dismissed by the Nyse Euronext board, which branded the offer risky and "strategically unattractive" and reaffirmed its commitment to completing the Deutsche Boerse deal.
The rejected suitors insist that they are confident of overcoming any regulatory hurdles, and are now promising to pay a "reverse termination fee" of $350 million if they fail to obtain the necessary antitrust and competition approvals.
The pair also say they have received fully committed financing of $3.8 billion from a group of firms to finance their offer.
In a letter to Nyse Euronext chairman Jan-Michiel Hessels, Nasdaq OMX and ICE reject the arguments against a deal, insisting that dealing with two partners, one focused on the cash equities business and the other on derivatives, is a better option than the "exchange supermarket" on offer from Deutsche Boerse.
"We believe that your stockholders should be given the opportunity to make the decision as to how best to allocate their interests in Nyse Euronext," says the letter.