More protests are expected to happen along the election campaign trail, the National Party's campaign manager says.

Both National and Labour launched their campaigns at the weekend, with hecklers out in force.

Some protesters had to be removed from inside central Auckland's Aotea Centre where Labour was hosting its campaign launch on Saturday while protesters were outside as National kicked off its own campaign at the Due Drops Event Centre in south Auckland's Manuaku on Sunday.

"What will be will be," Chris Bishop told Morning Report on Monday.

"National didn't have any protesters inside our launch. Yep, there was a few radicals and yahoos outside, yelling some stuff outside the venue but that's democracy, that's free speech, that's all good, they're entitled to their views, and Christopher Luxon was able to deliver his speech without any protesters inside the venue so that was good."

"There was a huge atmosphere there for the National Party and we enter the next 40 days in good heart and in good confidence."

A protester at Labour Party's campaign launch on 2 September. Photo: Craig McCulloch/RNZ.

Bishop says the disruptions so far had not made the party look at the diary and reschedule events, but it was taking the necessary precautions as would be expected from political parties during election campaigning.

It was expected that protests would happen as leaders are out and about around the country, he says.

"These things are going to occur. I'm sure it will happen again, there will be people who want to have a go and want to have a say. That's actually part of a robust democracy. We're taking the necessary precautions.

"I just encourage the people on the other side of the fence so to speak to just show a bit of respect for the democratic process and we've got free speech in this country, they're entitled to their views but leaders are also entitled to be able to go out and campaign and that applies to Chris Luxon but also, frankly, it applies to Chris Hipkins as well."

National Party leader Christopher Luxon announces the tax policy. Photo: Katie Scotcher/RNZ.

Tax policy can work - Bishop

Bishop is adamant the party's tax policy can work and that the party got advice before releasing it.

The Labour Party and tax experts have questioned whether the proposed tax on foreign home buyers can be enforced.

Bishop says he is extremely confident it can be done, despite international tax agreements New Zealand is signed up to.

He says it will only be for non-residents buying properties worth more than $2 million.

"We have been consulting with a range of economic, legal and financial and tax experts in the development of our policy, and we are extremely confident what we are proposing can be done and it will be done under National.

"At the end of the day, we are a sovereign nation, we are a sovereign country, we set our own rules and we are saying that if you want to come and buy a property here, over $2m, you have to pay at point of purchase a 15 per cent foreign buyer levy."

Bishop says the policy was not "radical", nor was it new, illegal, or something likely to cause problems internationally.

It was for non-New Zealand residents who wanted the "privilege" of owning property in the country without being a resident.

It would benefit New Zealand as many of these foreign buyers would also want to own businesses here - and employ New Zealanders.

- RNZ.