Social Development Minister Paula Bennett yesterday announced former Work and Income boss Ms Rankin had been appointed to the commission, set up at the behest of United Future leader Peter Dunne as part of a post-2002 election deal with Labour.
Mr Dunne has condemned her appointment as a commissioner, saying it was "untenable" and "grossly unsuitable", and it would be disruptive to the commission's work.
Ms King said Mr Dunne should be worried.
"National said they would get rid of the commission and it now looks like they've brought in Christine Rankin to bring it to its knees."
The appointment came on the same day that the Ministry of Social Development (MSD) announced it would shed 200 jobs -- a "slap in the face" for workers given the culture of extravagance Ms Rankin had overseen when she headed Work and Income, Ms King said.
Spending had included $1 million on a new logo and rebranding of her department, $80,000 on roadshows, $25,000 on self-promotion videos and $235,000 on a conference.
"What message is she (Ms Bennett) sending to the 200 hard-working MSD staff who have just learned they will lose their jobs by announcing the return of the person who brought the social welfare into ridicule and disrepute?"
Green MP Sue Bradford, whose anti-smacking bill was vehemently opposed by Ms Rankin, said the appointment was a "form of political sabotage".
The bill removed the defence of reasonable force in child assault cases and Ms Rankin was spokeswoman of For The Sake Of Our Children Trust, which opposed it.
She also caused a stir by calling former Prime Minister Helen Clark childless and saying Maori needed to face up to what a big problem child abuse was for them.
The Child Poverty Action Group was also "deeply unhappy" about Ms Rankin's appointment.
"At a time of recession biting and deepening poverty of many families in New Zealand, National hasn't grasped the seriousness of the mess we are in," spokeswoman Susan St John said.
"The appointment of someone who has a record of blaming families for their own poverty to a position where they are supposed to advocate for those same families is alarming."
But Ms Rankin said she would be accepting the appointment.
"I am surprised... I guess if you say things that upset some people or that people agree with you are going to be controversial," she told NZPA.
"Good heavens, they must be really scared of my views."
Lobby group Family First NZ welcomed Ms Rankin's appointment, saying it would "bring the commission down to earth".
It is understood Ms Rankin's appointment was hotly debated in cabinet.
