The probe is being conducted under state laws in New York, Connecticut and Maryland, Richard Blumenthal, Connecticut's attorney general, told CBS Radio News.
"The pressure is absolutely unprecedented and almost violent in nature [and] that raises the specter of joint activity," he said in a telephone interview.
Earlier this month, Smith & Wesson agreed to include safety locks with all handguns and pistols - external locks will be on the weapons in 60 days and internal locks installed within two years. New firearms would not be allowed to accept magazines that hold more than 10 rounds of ammunition.
The company also agreed to devote 2 percent of firearms revenues every year to developing "smart" technology that limits a gun's use to its rightful owner. The gunmaker, in addition, will not advertise or market its products in a way that appeals to juveniles or criminals, such as ads claiming guns are fingerprint-proof.
In exchange, a number of municipalities, states and the federal government agreed to drop threatened lawsuits over gun violence.
Other gun manufacturers and dealers opposed to the settlement have since put financial pressure on Smith & Wesson, based in Springfield, Mass.
A top wholesaler will no longer carry company weapons, retailers will not sell Smith & Wesson products and the National Rifle Association has accused the company of surrendering to Clinton administration demands, the New York Times reported.
"What is so anti-competitive about these potential agreements is that it strikes or retaliates against a company for seeking to bring a safer product to market," Blumenthal told CBS News.
"We are seeing behavior on the part of Smith & Wesson's competitors that raises the specter of illegal antitrust activity," New York Attorney General Eliot Spitzer said. "This is serious stuff."
Robert Delfay, president of the National Shooting Sports Foundation, denied the accusation.
"I could not be more confident that these are just independent actions by businessmen," Delfay said.
Blumenthal said more states were expected to become involved and subpoenas were imminent.
"Just as we sued the tobacco companies, our antitrust laws apply to collusion or conspiracy that seeks to retaliate or prevent a company from producing a safer firearm," Blumenthal warned.
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