Dan Lydiate says Wales will be made to pay if they do not keep their penalty count down against Ireland on Saturday.
Wales are currently giving away 13 penalties or free-kicks a game on average and have so far collected three yellow cards - two more than any other team - in this year's RBS Six Nations.
A repeat performance at the Millennium Stadium could see them punished by the boot of prolific Ireland fly-half Ronan O'Gara.
The 34-year-old needs only one more successful kick to take him across the 1,000-point barrier in international rugby and Lydiate is well aware of the danger he poses.
"Discipline is key," the Newport Gwent Dragons flanker said.
"We know we can't give away penalties, especially playing against someone like Ronan, who will kick them all day. We just can't give away as many penalties as we have been giving away.
"You have to be street-legal - we can't have men off the field. Our penalty count, the statistics are up there plain to see, and we can't shy away from how many we've given away.
"A lot of penalties, especially in the contact area, it is a fine line. They can go either way - you can either be a hero or a villain.
"It's hard, especially for an openside flanker. They live on the edge in games, and it's trying to find that fine balance."
Wales assistant coach Rob Howley echoed Lydiate's comments, warning that any more yellow cards could cost the hosts dear.
"We beat Ireland in 2008, lost by two points in 2009 and then last year a yellow card cost us points," Howley said.
"Yellow cards are a no-go zone for us, and I am sure it is equally the same with Ireland.
"The physicality of the international game is so important - the inches, the yards - and it's about keeping your head at those times when you are in defence.
"Sometimes you have been defending for a period of time and you have the ball in attack and you make an unforced error, and similarly when you have been in attack and then you go on defence, you make an error of judgement in terms of discipline."