Private jet companies in the UAE are warning their customers to watch out for competing airlines operating in the so-called "grey market".
Some companies that have launched or expanded in the country say they have invested large amounts in local infrastructure development while trying to attract passengers on to their planes, which tend to be much smaller than commercial airliners and cater to corporate executives.
Yet some competitors, they argue, are flying in from across the Middle East to pick up business but do so without holding the right kind of licence, known as an air operator's certificate.
"The problem is the policing of that," said Dave Edwards, the general manager of Gama Aviation, a business air operator from the UK that has expanded into the UAE.
"There isn't much policing that goes on in the Middle East to protect incumbents and home-grown carriers," he added, "and so we see an awful lot of foreign aircraft coming in and operating in our region who aren't legally allowed to do so."
While the industry does not track how much revenue overall gets diverted to grey market players, Mr Edwards estimated it was as much as 30 to 40 per cent of his company's business.
Other companies that are members of the Middle East Business Aviation Association, an industry group, said they were warning their customers about certain travel insurance implications.
When it comes to passengers who fly on private planes that are not supposed to be operating commercially, "there would be no insurance coverage if they were injured," said Mike Berry, the managing director for ExecuJet Middle East, which has offices in Dubai.
Insurance companies cannot pay for incidents that occur on illegal charters "precisely because the incident occurs during an illegal act", said Aoife O'Sullivan, a partner at Gates & Partners, a law firm headquartered in the UK that specialises in the aviation industry.
Larger international carriers have been trying to protect their markets by restricting landing rights, including those based in India, Germany and Canada.
But smaller operators argue their battle is different in that they are not competing with other companies legally picking up business in the UAE. "It is not a sense of protectionism for ourselves," said Mr Edwards.
"In this market, everyone has to be very 'fighty' about getting as much work as they can, but when the law is so clear on it, I don't think any of us should sit back and say, 'this is fine.'"