Transport Minister Michael Wood says it is "totally unacceptable" for protesters to disrupt Wellington commuters and the transport network.
Restore Passenger Rail activists sat on the south-bound lane of the urban motorway this morning, causing traffic to back up to Ngauranga Gorge.
They held a banner and handed out flyers to stopped motorists, calling for the restoration of passenger rail.
The flyer said the protesters were "sincerely sorry" for the disruption but climate change could not be ignored.
Spokesperson Michael Apathy said the group wanted the government to increase rail coverage to what it was in 2000.
"Kiwis really want their passenger rail service back," Apathy said.
"There's a bit of freight happening on the tracks, there's a bit of unsubsidised tourist lines, but it seems like successive governments have really wanted to prioritise private car use, which means that people who either don't want to drive or can't drive don't have very good options."
The group's calls for a better rail network hadn't gained traction so far, he said.
"We've given fair warning to the government - we did that a few weeks ago with a few MPs outside of parliament saying here are our asks and we really want some kind of response and a commitment, and so far we haven't heard a single thing back from them."
He warned the group had more action planned.
But the minister said the government had put $8.6 billion into rail since 2017, and introduced the first regional service in a decade.
"Much of this is the bread and butter of our network replacing track, new culverts and bridges, upgraded turnouts, all of which are needed for a safe and effective network," Wood said.
"This is also crucial work ahead of considering whether we introduce additional freight and passenger services across the network," he said.
"We have also introduced Te Huia, the first new regional rail service in a decade, to help build the case for additional regional and inter-regional rail services."
The government had worked well with many rail advocates, he said.
"However, these protesters are undermining their cause and frustrating the public, when they should be working to build public support for future rail investment."
His office confirmed Wood had seen a copy of the group's letter but was not part of the cohort who received it outside parliament.
Police removed the handful of protesters about 8am and escorted them to a police van.
One man, whose hand earlier appeared to have been glued to the road, was carried by four officers.
Wellington area commander inspector Dean Silvester said the protesters' actions were dangerous for them and motorists.
"We will not hesitate to take action in cases where safety is threatened."
Six people were charged with wilful trespass and criminal nuisance.
In the Wellington District Court this afternoon, they were remanded on bail on condition that they do not obstruct any public accessway or encourage any illegal protest activity.
They will appear again in court in three weeks.