European members of Paragon are angry over the decision by the US National Business Travel Association (NBTA) to stage a two day conference in Milan next year.
A source told BTE that the decision had been made without any consultation with Paragon members.
He said members were "dumfounded" by the decision and deciding what to do next.
One organisation, the UK and Ireland Institute of Travel Management (ITM) has pulled out of its planned partnership forum with the Americans due to be held in London next month.
The source told BTE that Paragon, an umbrella organisation representing travel managers' associations, met last week during NBTA's annual convention in Boston.
"We were not consulted about the Milan conference and it has obviously confused European members. Europe would have expected a little bit of consultation.
"I am not totally surprised. We have seen the NBTA and their global actions so sooner or later I knew they would arrive in Europe.
"We are kind of dumfounded. It is an unspoken code of behaviour that Paragon members do not move into another member's area.
"We are still trying to evaluate this new situation. We are trying to get the Americans to make a statement so that Paragon can make a decision about its future."
A spokesman for ITM said the association had written to its members saying it would no longer be in partnership at the planned event on September 28.
He said that "owing to the uncertainty of NBTA's future actions in Europe and the impact on ITM, we though it was not appropriate at this time to be involved with them in this type of event until NBTA's position is clearer."
The spokesman added that it was not discouraging its members from attending the event and they would still get an advantageous rate.
"We are not saying we will not talk to them in future, we are not closing down our relationship with them or throwing our toys out of the pram. But we feel it is not appropriate at the moment.”
The NBTA said the London conference would still go ahead despite ITM's withdrawal.
Bill Connors, the association's executive director and chief operating officer, said: "We are still having the event despite the disappointment of ITM pulling out. But that was a business decision and we respect them for it."
He confirmed that ITM would still get a discounted rate if they attended.
Mr Connors said the Paragon claim that it had not been consulted was "not exactly correct."
NBTA, he said, had first proposed to hold a conference in Brussels which Paragon knew about.
But when this venue fell through, it had decided on Milan and had e-mailed Paragon members on June 26.
Mr Connors rejected the charge that NBTA was moving into other members' territory.
"We are a global organisation which holds eight different events a year. We purposefully chose Italy which is not a Paragon member. We are staying out of Paragon territory."
But he stressed that NBTA was still talking to Paragon and he was hopeful that they could go on working as partners.