Several law firms are targeting NYSE Euronext's (NYX) planned acquisition of trading technology company Nyfix Inc. (NYFX), suggesting that the $144 million deal could be unfair to Nyfix shareholders.

The Law Offices of Howard G. Smith and Finkelstein Thompson LLP both announced late Friday that they were opening investigations into the deal, seeking to recruit Nyfix shareholders as they mull legal action.

The announcements come after Wolf Haldenstein Adler Freeman & Herz LLP revealed on Aug. 28 its own inquiry into the planned acquisition.

An NYSE Euronext spokesman declined comment Friday.

The transatlantic exchange operator moved last week to acquire Nyfix, a provider of brokerage services and trade stations, planning to purchase its shares at $1.675 each, a 95% premium to the Aug. 26 closing price.

The firms' investigations center on the fairness of the price NYSE Euronext will pay for Nyfix, which includes preferred stock. In a release, Finkelstein Thompson LLP noted that shares in Nyfix were $3.75 one year ago.

Nyfix's stock has been badly beaten down in the financial crisis, declining 74% for the past year through Aug. 26. But the last 12 months only steepened what has been a multi-year slide for Nyfix shares, which traded above $45 in 2000. Shares closed Friday at $1.64.

Upon closure of the transaction, expected in the fourth quarter, Nyfix will become part of NYSE Euronext Technologies. The exchange operator looks to tap into Nyfix's established network of pension funds and asset managers that rely on the company to facilitate pre-trade communication with brokers.

NYSE Euronext shares closed about 1% higher Friday at $27.61.

-By Jacob Bunge, Dow Jones Newswires; 312-750-4117; jacob.bunge@dowjones.com