Organisers of trade shows across Europe have warned exhibitors about the activities of an Austrian company that charges €971 for entries in what Britain's Association of Exhibition Organisers (AEO) describes as a "worthless online directory".

Construct Data Verlag - whose mailshots target companies in Europe, Asia and the US - has also attracted the attention of the European Advertising Standards Alliance (EASA). The Austrian Trade Commission in London said it had received many complaints about its activities.

Mr Trevor Foley, AEO's chief executive, said his group had been "inundated with exhibitor complaints" about Construct Data's Fair Guide. He urged exhibitors to ignore demands for payment.

In a letter to AEO members, Mr Foley said Fair Guide used "a deliberately confusing form which looks like an organiser's free listing service.

Companies that sign and return the form are then billed €971 for a worthless online directory entry which quickly escalates into intimidatory debt recovery tactics and threats of legal action."

In June, EASA said the Austrian Advertising Council had twice investigated Construct Data's mailing and found it to be misleading and in breach of the country's advertising code.

Construct Data continued to distribute it unchanged.