Animal testing group Huntingdon Life Sciences (HLS) has demanded an explanation as to why the New York Stock Exchange (NYSE) halted its debut.
Huntingdon bosses were reportedly taken aside by the NYSE's president
Mike Caulfield, general manager of its US headquarters in New Jersey, said they had been given "scant information" about the exchange's decision.
Reports claim the NYSE received calls warning it could be threatened by animal rights activists opposed to HLS.
But NYSE would only confirm the firm's floatation had been postponed.
Just 45 minutes before shares in Life Sciences Research - the US parent company set up by HLS - were due to begin trading on Wednesday, HLS executives were taken to one side by the exchange's boss and told the listing had been postponed.
Mr Caulfield added: "What happened? You'll have to ask them. We are still trying to find out and have asked for an explanation but so far have got nothing," Mr Caulfield added.
Meanwhile, HLS chief executive Brian Cass told Channel 4 News he was "disappointed, distressed and astonished" by the move.
HLS quit the London Stock Exchange in 2001 after fierce protests.
The company moved its headquarters to the US after a sustained - and often violent - campaign by animal rights protesters in Britain.
Huntingdon boss Brian Cass said he was puzzled by the decision
"Obviously we were greatly disappointed," Mr Cass told the BBC.
"There have been threats from various aspects of the animal rights movement both in the UK and the United States, but whether that is the issue or not, it is something the exchange must answer."
He later told Channel 4 News that there had been a lot of conjecture surrounding the pulling of its US listing - but nothing had been confirmed.
"I think the real question now turns to the NYSE and why it's done this - could it happen again to other companies?" Mr Cass added.
Investors in New York also expressed surprise that the US exchange had apparently caved-in to pressure from protesters, although one activist group described the move as "another slap in the face" for Huntingdon.
Meanwhile, one US senator has also reportedly come forward to say that the exchange should not give in to animal rights campaigners.
HLS said the company's day-to-day operations would not be affected by the sudden pulling of its New York listing.
"It's not the first time we've been at the centre of a storm," he said.
Activists have protested against a number of companies involved in animal testing in recent years, targeting shareholders and businesses connected with laboratories.
The UK-based Stop Huntingdon Animal Cruelty campaign focused its efforts on Huntingdon's suppliers, many of which eventually severed their ties with the company because they feared getting bad publicity.
The government has since said it plans to clamp down on animal rights activists intimidating company employees, shareholders and suppliers.
Despite the decision by the NYSE, trading in Life Sciences Research continued on the US Nasdaq index's electronic over-the-counter market.