Wales have followed Scotland's example by refusing to participate in a Great Britain football team at the 2012 Olympic Games in London.
The FA of Wales wants to protect its identity as a separate nation
The Football Association of Wales said supporting such a team would threaten its status as an independent nation.
"The FAW will not undertake anything that would jeopardise its position as a separate nation within Fifa and Uefa," said FAW secretary David Collins.
England and Northern Ireland have said their players will be made available.
The idea of reforming the British Olympic team was suggested by the Football Association in July.
Last month, British Olympic officials said the team would still go ahead even without Scottish involvement.
Wales' withdrawal, which was announed on Tuesday after an FAW council meeting in Ewloe, is unlikely to change that view.
Sepp Blatter, president of world's football governing body Fifa, assured the home nations that taking part in the 2012 Games would not affect their separate identity in world football.
But Collins says the FAW has never received a written assurance and fears Fifa's stance could have changed by the time of the London Games.
Collins added: "Wales doesn't want to compromise its position as a separate nation within Fifa and Uefa.
"It wants to continue playing football internationally as Wales.
"And I must say that everything I've heard from the Welsh media and the supporters in Wales fully endorses the [FAW] council's decision."
London 2012 organisers have already identified Cardiff's Millennium Stadium as a possible venue to host some of the football games.
Organisers had also promised the first event of the Games - the opening football match - would kick off at Hampden Park, Glasgow, if the Scots supported the idea of a British team.
The Great Britain team would be limited to players aged under 23 but three overage players would be allowed.
Britain won the gold medal in football at the 1908 and 1912 Games.