Cabinet minister Chris Tremain is to stand down at next year's election - and Prime Minister John Key has indicated other National MPs will follow.
The Napier MP, 47, said he is quitting to spend more time with his three teenage children.
Key said Tremain told him of the decision two weeks ago, and it was "a little bit of a surprise".
"I'm always shocked by the odd, sort of, retirement that comes along. The last election we had a few."
He was aware of "one or two" MPs who would not stand next year - although he was not saying who.
"We always get a few, we've got a caucus of 59, so they'll be a few. We are not forcing the pace on it."
Tremain had done a "tremendous job" in his nine years in Parliament and would be missed, he said.
"He won the seat of Napier that we hadn't won for 50 years ... but I can understand completely.
"He's a young man, he's got a relatively young family, he'd got some strong commercial interests he wants to follow and he feels he has made a good contribution and it's time for him to go and do something else."
Key admitted it will be "tough seat" to win, but the party vote was more than 6000 at the 2011 election.
Former MP Stuart Nash will stand for Labour.
Tremain said he wanted to finish several "local projects" before the end of the parliamentary term, and to push through local government and gambling law reforms.
"My family has been a huge part of my decision. I have three children finishing high school and I want to devote more time to them before they leave home," he said.
He decided to make the announcement now to allow the National Party time to find a suitable candidate to contest the seat.
"In the last election, I had a 6600 party-vote majority and a 3700 electorate vote majority, which I believe provides a solid platform for a strong National Party candidate to win Napier once again in 2014," he said.
The former accountant and estate agent first came to Parliament in 2005, beating incumbent Labour MP Russell Fairbrother by 3951 votes. He was the party's chief whip, and then consumer affairs, local government and civil defence minister outside Cabinet.
In April last year he was promoted to Cabinet as internal affairs minister, after the resignation of Nick Smith.
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