A campaign text message sent out by one of Paula Bennett's volunteer workers is causing a problem - it contained the mobile phone numbers of 40 people.

National's deputy leader says it was part of her party's normal phoning and texting of voters.

"Unfortunately, one lot went as an iMessage which means the 40 numbers could be seen," she said.

"No names or any other details were disclosed."

The message, however, said the mobile numbers came from the electoral roll.

That's been denied, with a party spokesman saying they were gathered "through a range of different ways".

The Electoral Commission confirmed it had received a complaint about the text and would be looking into it.

"It is factually incorrect to say that phone numbers are from the electoral roll," a spokeswoman said.

"The Commission would like to assure people that phone numbers provided to the Commission are not released to anyone."

The offending text read: "Hi. I'm Paula Bennett, your National candidate. I got your number from the electoral roll. National are a strong team. We want to continue to grow NZ & take the next step in tackling hard social issues. We know what needs to be done & how to do it. Please support me and the National Party. Paula."