The number of overseas property owners based in the UK currently using HomeAway could fall by a fifth if controversial new tax proposals are implemented.
HomeAway says a survey of existing owners on the site found that 17% would consider not renting out their properties in the future if the UK government's proposal to end "loss relief" ends next year.
The current system allows property to offset some elements of tax on overseas properties for work carried out using capital, such as structural improvements.
However the new coalition government is reviewing the existing scheme, known as the Furnished Holiday Lettings rules, ahead of changes to come into effect in April 2011.
Another proposed change will mean owners will have to ensure properties are rented for 15 weeks a year, a jump from the current ten-weeks.
The owner survey also found that 56% would have to increase their rental rates if proposals were accepted.
A HomeAway UK official says the company is seeing "large amounts of organic growth every year" and while there is always "natural loss through people selling properties or stopping renting for other reasons", any damage to HomeAway will be offset by new properties entering the market.
"There is still huge scope for growth in this industry so although this may be a set-back, it would be more so for the individual owners affected."
The company says it will help owners to achieve the minimum rental period of 15, stressing that the majority of those on its system "easily achieve this".
"We also hope that, as the government works to change the tax regulations that affect the letting of holiday homes, they will remember that holiday rentals help local communities by bringing in tourists, who go to local shops, eat in local restaurants and visit the local attractions."
Rival holiday rental firm, TripAdvisor-owned HolidayLettings, says any changes should be seen as an opportunity.
"The extended advertising period gives every holiday home owner an opportunity to review and optimise their marketing strategy, something that any profitable business needs to do regardless of industry.
"Also, by keeping the Furnished Holiday Letting tax treatments relatively unchanged, but tightening the eligibility criteria, the proposals will continue to protect the professional holiday home landlord while increasing the incentives for part time landlords."