The Welsh Rugby Union (WRU) will ask the International Rugby Board (IRB) to rule Steven Shingler ineligible to play for Scotland at the forthcoming Six Nations.
The London Irish fly-half was called up by Andy Robinson to his squad for the opening fixture with England on February 4, one of six uncapped players in the 36-man pool.
With Shingler having previously represented his native Wales at Under-20 level, the WRU raised a dispute over the eligibility of the Swansea-born player to switch his allegiances.
"The International Rugby Board can confirm that it has been contacted by the Scottish Rugby Union and Welsh Rugby Union regarding the eligibility status of Steven Shingler," a statement from the IRB confirmed.
"It would be inappropriate to make any further comment until the matter has been fully reviewed and the Unions informed of the outcome."
The Scottish Rugby Union (SRU) insist they have followed protocol to name Shingler in their squad.
But, following a statement from the Scots last night stating the player refused to sign a declaration to commit him to Wales, the WRU have refuted their claims and have called on the IRB to have the final say.
“Steve Shingler played for Wales U20s against France in 2011 before which he was specifically informed, as were his fellow squad members, that the match would confirm their sole qualification as potential Wales senior international candidates,” a statement from the WRU read.
"Shingler was told by the U20 team management that if he played in the game he would become a Wales qualified player and therefore ineligible for selection for any other nation.
"The regulations and guidelines relating to qualification compliance are set in accordance to IRB regulations and any questioning of these regulations should be directed to the IRB.
"We have made the IRB aware of this issue today and will be returning to it as a matter of urgency in the morning."
Under IRB rules, a player cannot change nations once he has represented the “next senior” international team for one country.
While this is typically an ‘A’ representative squad, Wales disbanded their second string in 2003, making their Under-20 squad their second tier.
Shingler qualifies for Scotland through his Dumfries-born mother and the SRU claimed on Thursday night that the player himself was clear he had the right to switch nations.
An earlier SRU statement read: "Steven has informed us that he made it clear that he wished to leave open his international eligibility as he was also eligible to represent Scotland and England as well as Wales.
"Scottish Rugby believes we have acted in good faith in this matter and have also taken cognisance of an IRB ruling last year concerning two players who played for Wales under-20 against France under-20 in 2010 who now play for Connacht and are eligible for Ireland. We are liaising with the IRB on this matter."