The New York Stock Exchange (NYSE) has been accused of caving into threats from animal rights activists.
Animal rights activists have widely targeted HLS
The claim came from Life Sciences, the US parent firm of animal testing group Huntingdon Life Sciences (HLS), at a US Senate hearing on "eco terrorism".
The company focused on the effect of the Stop Huntingdon Animal Cruelty campaign (SHAC) on businesses.
Life Sciences said it was "patently clear" the SHAC campaign had led the NYSE to postpone its share listing.
During the hearing, Life Sciences and the NYSE were questioned about the decision to postpone the company's listing minutes before its debut.
NYSE representative Richard P Bernard apologised for the timing of the postponement, saying: "We got our cart before the horse."
However, he added that the reasons behind the decision were "confidential" but also pointed out that the exchange had the right and said that under SEC rules the exchange could "bring in other factors to determine a listing".
The exchange was still looking into the listing of Life Sciences, he said.
But Life Sciences' general counsel Mark Bibi told the hearing that when he met NYSE officials on 7 September - the day of its planned listing - they only spoke about a planned campaign by animal rights activists.
"It was patently clear to me that the only reason the NYSE postponed our listing was because of concerns about the SHAC campaign," Mr Bibi said.
He added that the decision to postpone Life Sciences' listing only 45 minutes before its shares were due to begin trading had affected its stock price.
Its shares had stood at $17.50 on 6 September on the Nasdaq bulletin board, but since the postponement they have traded as low as $8. On Wednesday they closed at $12.25.
Huntingdon Life Sciences has been targeted for years by animal rights activists.
Senior executives have been physically attacked while others with links to the company have been subjected to serious intimidation - developments which led to the firm moving its headquarters from the UK to the US.
However, the aggressive campaign of harassment has continued across the Atlantic, according to reports.
Traders buying and selling their shares were targeted and when Life Sciences applied for a listing on the NYSE, the exchange itself reportedly became the focus of animal rights activism.