ACT leader David Seymour has delivered a billion dollars of fake money to a teacher's union in the hope it might persuade them to support his policy to increase salaries.

Mr Seymour had the fake cash printed - with his own face on it - and took it to the NZEI's headquarters in Wellington today in a wheelbarrow.

"Teachers have been underpaid for a very, very long time," he told reporters.

"We're offering to raise teacher pay by $20,000 on average and let schools and boards decide how much to pay their teachers."

Mr Seymour said there was a critical teacher shortage across New Zealand and something had to be done.

"Their maximum is $78,000 and everyone gets paid the same," he said.

"They need the opportunity to see what a billion bucks looks like."

Mr Seymour wheeled the money into NZEI's reception and was told to leave it there, which he did.