Police are investigating death threats to anti-smacking campaigner Sue Bradford.

One warned the Green MP that she could be New Zealand's "first political assassination".

Police are now looking at stepping up her personal security after the threats to kill on Twitter, the Sunday News reported today.

"There has been a whole lot of stuff. Some of it is pretty nasty," Ms Bradford said

The architect of the anti-smacking legislation said she had "become the iconic symbol for the opponents, for the people who want to change the law back".

"I have been copping it for four years. I copped it for many years earlier on for standing up for unemployed people and beneficiaries and being a street protester. It is what happens when you stand up for what you believe."

She has moved house several times to protect her privacy. She also has special dispensation from Parliament to leave her name and address off the electoral roll.