Local MP Simon Hart has written to the organisers of Ironman Wales to encourage them to keep the event in Pembrokeshire.
Ironman UK agreed to hold the Wales event in Tenby until 2015 and although the company has said "it can see no reason not to return", the contract has not been signed.
Writing to Kevin Stewart, Ironman UK Managing Director, Mr Hart said: "Firstly, may I congratulate you and your team on organising a wonderful event in Tenby on September 14. I spent the whole day in Tenby with my family, two of whom were competing, and the atmosphere was second to none.
"I am writing to you to say how much we all hope that IronMan Wales will stay in Pembrokeshire beyond 2015. I understand that, while the event is signed up to Tenby until 2015, after that date it could move within Wales.
"I sincerely hope that the incredible support that the people and businesses of Pembrokeshire give the event help to keep it in the county for many years to come.
"All the feedback that the athletes have left about the event on Facebook, in triathlete forums and blogs, talk about the special atmosphere at IMWales which is created by the incredible public support on the day.
"40,000 people in Tenby on the day, including thousands at the start of the swim at 7am, show that this is an event that has truly captured the imagination of local people.
"I know that this is a commercial decision for you, but I hope that the popularity of the event, with so many local athletes wanting to compete and so many residents turning out to support, will help to safeguard its future in Tenby."
Simon Hart MP
House of Commons
15, St John St
or 0207 219 3000