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Tew told the Otago Daily Times yesterday the union has an active drug-testing policy, and wants drug-free sport.
''We know what we want. We have worked very hard to get it and if there is more to do then we will keep doing it,'' he said.
''We have a very close working relationship with Drugfree Sport New Zealand and we run a comprehensive drug-testing campaign,'' he said.
''But we know if people want to cheat there is a way round the system. I do not think that there is a problem in New Zealand but we do not want to be complacent.''
The NZRU carried out both in-competition and out-of-competition testing.
An elite group of players were on 24-hour notice. Those players had to tell a drug agency where they were for the next 24 hours.
''So if you change your holiday plans and are in the wrong place then you can have a real problem. We work really hard at it but ultimately there are things we could do better and we will have a watch on it.
''As we have seen in other sports, such as cycling, if people want to cheat they will find a way to do it, particularly when there is big money involved. We would like to think we have got a system in place that has worked.
''But players make mistakes. Drug cheating is not always about deliberate actions, either. I have a child in a high-performance sport too, and they have to be vigilant in all what they eat and drink.''
Tew said the report released in Australia by the Australian Crime Commission last week had cast a shadow over all sports which he thought was unfortunate.
Tew was at the launch of this year's Super 15 season on a stifling Auckland day which hardly seemed suitable weather for the winter game.
He acknowledged in an ideal world the season would start two to three weeks later. But with what the rugby union had to do over a year and how it had to fit in with other unions the season started when it did.
Ultimately, it came down to whether the games were any good at this time of year, Tew said.
''If the games are good footy, if the new rules work and we see some good close encounters then it won't be too early, will it? People I am talking to can't wait.''
New laws will include a new scrum engagement, the five-second rule around releasing the ball from the back of the ruck, seen in domestic rugby last year, while the third match official will have more power, including ruling on some judicial matters.
Tew said the jury was still out on giving more power to the third match official.
''Ultimately, there is going to be an element of human judgement in our game. You want to give the referees the best possible chance to perform well in a collision-oriented sport played at an incredible pace under a complicated set of rules.
''So we want to make it a little bit better with the use of technology. But we are not going to get too carried away with it either.''