Scrum-half Mike Phillips has been suspended indefinitely from Wales squad duties, the WRU announced today.
The 28-year-old has been banned "with immediate effect" following allegations of an incident involving the player in Cardiff city centre.
A statement from the WRU read: "The Wales management team will take time to consider circumstances surrounding recent allegations about the player's behaviour in public whilst on an agreed holiday period from pre-Rugby World Cup training.
"Phillips has been told not to report to WRU headquarters at the National Centre of Excellence this Monday - the pre-ordained start date of his personal training regime - and will remain outside of the squad until further notice."
Phillips, who sealed a move to French Top 14 club Bayonne from Ospreys earlier this week on a two-year deal, is now expected to face questions over the allegations.
"The WRU operates to its own strict code of conduct covering behaviour both on and off the field, in circumstances of serious indiscipline the national squad management have the capacity to impose sanctions on players for matters arising from occasions when they are not on official squad duty," the statement continued.
"Whilst the suspension is in operation further clarification regarding the incident will be sought.
"The suspension has been approved by Wales head coach Warren Gatland and agreed by the senior squad management team. The WRU has not been alerted of any criminal action and the suspension is based on its own behaviour protocols."
WRU chief executive Roger Lewis explained Phillips's suspension was a result of a "breach of standards".
"Discipline and acceptable behaviour are issues which run to the core values of the Welsh Rugby Union and we cannot tolerate any compromise of those standards," he said.
"Mike Phillips is an exceptional player, but there is irrefutable evidence of a prima facie nature that he was engaged in behaviour which falls below the standards we set.
"It is vitally important that we send out a clear and unambiguous message to one and all concerning our views on matters of this sort.
"That message must be heard clearly by all players, coaches, administrators, volunteers, supporters and, of course, the parents and guardians of any child attracted to take part in the national sport of Wales.
"By taking decisive action now we are emphasising that this sort of incident is highly unusual in that the majority of people involved in Welsh rugby help us maintain the proud record we have for fair play and off the field courtesy.
"Our senior national squad players are highly visible because of the profile which accompanies the success of our national sport and it is made clear to them that they are the ambassadors we rely on to foster and sustain our image.
"An incredible amount of hard work is currently taking place as our players prepare for the Rugby World Cup in New Zealand and that effort must be recognised and supported by all involved.
"I am making my views public at this time because, as the nation anticipates our involvement in Rugby World Cup there is no room for any ambiguity in our reasoning.
"Rugby is part of the culture of our nation and we must do all in our power to ensure that the game remains a sport that everyone in Wales can be rightly proud of."
Phillips has been replaced by Lloyd Williams in Wales' pre-World Cup training squad.