David Parker is promising to push for an exemption to US tariffs on steel and aluminium.

The Trade and Export Growth Minister is in Washington DC and Ottawa this week, to talk World Trade Organisation reforms.

But Parker is keen to also address the tariff issue.

He said our trade is in balance with the US, and we're not "a country that screws the scrum".

Parker said he doesn't know why we've not been granted an exemption - when Australia has.

"There are other countries like Japan that have pleaded the case at the highest level with President Trump by Prime Minister Abe, but they haven't been successful in getting an exemption either."

Another issue top of Parker's list is the appointment of new judges to the World Trade Organisation's appellate body.

He said the US and some other countries have complained about how the appellate body is going about its work - enforcing international rules around trade.

New Zealand has some ideas for how to resolve those problems, he said.

"We share some of the USA's concerns, although we are a very firm in our view that the appellate bodies is useful to all countries, but particularly to small countries like New Zealand."

Outside of the US, Parker is keeping an eye on the continuing struggle between the UK and EU to forge a Brexit deal.

British Prime Minister Theresa May said next month's deal signing isn't going to happen and the transition period could be delayed beyond 2020.

Parker said our negotiators can't get cracking on a new agreement with the UK for when it leaves the EU.

He said "because the United Kingdom doesn't know the terms of their divorce from the European Union, we are a bit more in the dark as to what the details of an agreement with New Zealand can be as a consequence."