Scandinavian agents are meeting today (December 13) in Copenhagen to consider legal action against the International Air Transport Association (IATA)
The agents from Sweden, Norway and Sweden are also considering making a complaint against the Association to the EU.
The moves come after IATA's airline members voted last week at its Special Passenger Agency Conference in Singapore for weekly BSP payments in Scandinavia.
The airlines voted to shorten the payment period from monthly to weekly by 2010 despite strong opposition from the agents.
The agents say the decision will cost them €4.5m a year in lost interest.
The IATA decision has also been strongly criticised by ECTAA/GEBTA which represent leisure and business travel agents across Europe.
A spokesperson for ECTAA/GEBTA said it was exploring "all possible means to address this matter, including legal actions."
Its president Jan Van Steen said: "The unilateral decision to change agents' payment terms is in stark contrast with the recommendations made by the European competition authorities in the frame of the ECTAA/GEBTA complaint issued in 2002, which invited IATA and IATA airlines to negotiate jointly the requirements to operate as IATA agents and which should respect the principle of proportionality."
A statement by ECTAA accused IATA of ignoring the agents'opposition and of by-passing the "normal consultation through the local IATA bodies."
It added: "For agents, the change in payment terms will be extremely harmful as in many cases agents will have to pay the airline before they have received the money from their customer."
Mr Rolf Forsdahl, director of the Norwegian Travel Trade Association, said his members would be holding a meeting in mid-January to discuss what action to take.
He said informal talks had already been held with the country's competition authorities and he was meeting his Danish and Swedish counterparts in Copenhagen today to consider legal action.
HE added: "There is no rush. We have time to consider our options and of course have a dialogue with our members.
"We want to see what chance we have of a successful court action and the cost. Any action we take will be co-ordinated."
Mr Lars Thykier, managing director of the Danish agents' association DRF, said: "We shall be opposing this all we can."