A COALITION Senator has launched an extraordinary attack on Labor frontbencher Penny Wong for betraying Julia Gillard and "the sisterhood".

Attacking Government legislation that will deliver pay rises to only some childcare workers, the Opposition spokeswoman for women, Michaelia Cash, said the Rudd Government had tricked staff into believing a pay rise was coming.

"The current Rudd Government, who we all know Senator Wong voted for," she said.

"The sisterhood stabbing one of their own in the back.

Making giant stabbing motions with her hands, she continued her spray.

"You've always got to like that, don't you? When the sisterhood stab one of their own in the back.

"Stabbing people in the back is exactly what this legislation does."

The legislation, which passed, sets up a $300 million fund to provide grants over two years to early childhood services to help them attract and retain qualified staff.

But the fund will only cover pay increase for between 27 and 40 per cent of childcare workers.

Finance Minister Penny Wong said voting for Rudd in the leadership ballot was "the most difficult decision of my political life".

Describing Ms Gillard as a friend, Senator Wong said she told the former PM of her decision beforehand but would not reveal how she took the news, only saying that she showed enormous dignity and class.