Clarke Gayford says he supports students protesting across New Zealand calling for action on climate change.
"Get bloody stuck in today kids. Wear any punishment like badge of honour," Gayford wrote in a tweet Thursday night.
The partner of Prime Minister Jacinda Ardern revealed in the tweet that he had seen a "constant stream of letters from kids on banning plastic bags".
The Government confirmed last year that retailers will be banned from selling or giving away single-use plastic bags from July 1 this year in a bid to reduce plastic waste.
Gayford said knowing the effect the ban had on inspiring young people, "don't let anyone tell you your voice isn't important".
Students across New Zealand are joining the global School Strike 4 Climate on Friday, organised globally by Swedish student Greta Thunberg and in New Zealand by Porirua student Sophie Hanford.
Gayford received mainly positive messages to his tweet, with one person telling him: "Well said. My daughter wants to go. School rules are they will get detention. She knows the consequences should she decide to go."
Another told Gayford: "It feels great to see the next generation own their future."
The strike has been met with scepticism by many who believe attending school is more important than striking, and that it should take place over the weekend instead.
Deputy Prime Minister Winston Peters told Newshub: "We pay a lot of money for people to get educated. Attending school is compulsory in this country."
National MP Judith Collins said last week it "won't help the world one bit".
The Prime Minister was more cautioned in her response, saying she hoped in New Zealand there is "less cause for protest" and that the Government is "trying to do our bit".
On Wednesday she joined Climate Change Minister James Shaw and students at Wellington College where she told those planning to strike not to "underestimate the power of your voice".
"I'd like to think we're already on board, we're ready and we recognise this challenge and we're doing what we can. But we need that to be reinforced and reinforced really strongly. So keep challenging all of us."
The movement has spread across the world, including Australia and the UK. It was announced on Friday (NZ time) that Greta Thunberg had been nominated for the Nobel Peace Prize.