Gloucester could face a fine, or even risk losing league points, for including Wales international Gareth Cooper on the bench on Sunday.
Cooper, who did not feature for Wales against Canada on Friday, was named on the bench by Gloucester coach Dean Ryan for Sunday's Guinness Premiership game against Saracens.
Gloucester's decision to use Cooper went against an earlier IRB ruling that said the Welsh Rugby Union did not have to release the player, who they wanted to attend a video analysis session on Sunday.
The scrum-half did not play for Gloucester, watching his side win from the bench, but if Wales complain the Rugby Football Union will be asked to investigate.
"Everybody involved in this situation knew of our decision when we took it at noon today," said the Gloucester coach, Dean Ryan.
A Welsh Rugby Union spokesperson said: "We are seeking to establish all the facts and once that is done we will consider all the material issues and act accordingly."
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