NEW South Wales conservative Christian MP Fred Nile says federal Finance Minister Penny Wong is setting a bad example by having a baby with her female partner.

Senator Wong today announced her partner, Sophie Allouache, is due to give birth in December after falling pregnant through IVF.

NSW Christian Democrats leader Mr Nile is opposed to same-sex relationships and children being raised by gay couples.

"I'm totally against a baby being brought up by two mothers - the baby has human rights," the upper house MP said.

"It's a very poor example for the rest of the Australian population.

"She needn't have made it public - it just promotes their lesbian lifestyle and trying to make it natural where it's unnatural.

"The only reason she's made it public is to make a statement to the Australian people."

Mr Nile, who has led prayers vigils during Sydney's annual gay Mardi Gras parade, called on Prime Minister Julia Gillard to have a "talk" with her cabinet colleague about her decision to publicise the impending birth.

"She should have a serious talk with her," he said.

But he also had words for the prime minister's unmarried status.

"Because of her own life, that puts her in a weaker position than if she was traditionally married herself," he said.

Mr Nile said he was surprised Deputy Opposition Leader Julie Bishop had congratulated Senator Wong.

"I'm surprised she's done that. She's treated this as if Penny Wong is in a traditional relationship," he said.

The NSW parliament last year passed legislation giving same-sex couples the right to adopt children.