Wales coach Warren Gatland has blocked Taulupe Faletau's proposed move from Newport Gwent Dragons to Bath.
The Dragons had sought to release the the 24-year-old forward, whose contract runs out in the summer of 2016.
Under the funding agreement for Welsh domestic rugby, Gatland has to sanction international players moving outside Wales.
A Welsh Rugby Union statement said they were committed to keeping the best players in the country.
The Dragons, meanwhile, said the decision was "disappointing".
WRU chief executive Martyn Phillips said: "Although there are circumstances under which moves out of Wales by experienced players can be sanctioned, Taulupe's status as a player and importance as a role model means we would like him to be playing his rugby here."
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