England's players' union are taking legal advice over a letter sent by the Rugby Football Union telling top stars they could be jeopardising their international places by moving abroad.

RFU chief executive Francis Baron warned in the note that crossing the Channel and playing domestic rugby in France could seriously hinder their futures.

The move has been prompted by the decision of London Wasps trio James Haskell, Tom Palmer and Riki Flutey to move to French clubs next season, sparking fears of a player drain to their Top-14 competition.

French clubs are not restricted by a wage cap which hampers English Premiership outfits in their attempts to increase wages.

In the four-page letter, Baron says that players must have all international release periods written into their French contracts and, most significantly, made it clear that if England team manager Martin Johnson was faced with a close selectorial choice between two players - one playing in France and the other at home - the Premiership player would almost certainly get the vote.

But the chief executive of the Professional Rugby Players' Association, Damien Hopley, said: "We are taking legal advice. The concern is that this becomes a restraint of trade."

Although the letter states any player moving abroad will not be "banned" from the England squad, it makes it clear they could jeopardise their places. It has also been made clear that Johnson and his coaching staff will not be travelling to watch players in the French league.

Hopley believes the whole situation is unfair. "On one hand the RFU says it's fine for players to go to France, on the other that it would not be as attractive," he said.

"You have to remember that it's not just a financial decision for players to go but also about lifestyle and experience. We were pro-active in seeking legal advice once we found out about the letter."

It was believed that the letter had prompted Haskell to reconsider joining Stade Francais, where Palmer is also destined. But Haskell has insisted he still wants to go and will be joined by Flutey, who is off to Brive, a club that already boast England internationals Steve Thompson and Andy Goode.

Sadly, Baron's letter shows that, once again, the RFU are being reactive over a major problem rather than pro-active. They knew France was a potential destination for leading players with the credit crunch affecting Premiership finances. However, instead of leading the debate, they have been left to try and catch up with the issue.Jonny Wilkinson has also been linked with a move across to France but that has been dismissed by his club Newcastle today.

Falcons director of rugby Steve Black said: "If Jonny or his advisers come to us with something concrete and say this is what's happening, then we take it from there."