Just one day after it was made official, there are calls to shelve changes to the code of practice for commercial television stations.

Television programs like the crime series Underbelly thrive on on-screen nudity and raunchy sex scenes. And while they attract controversy, they also corner huge audiences.

Now, the Christian group Family Voice Australia is worried that a new code of practice gives commercial TV networks the green light to push the boundaries of decency further.

Ros Phillips, the group's national research officer, says she is concerned that it waters down the guidelines to allow explicit pornography at 9pm, "when many children are still watching".

What has piqued her concern is a change to the guidelines for sex scenes in programs rated MA. Previously, the industry's code of practice required sex to be portrayed discreetly.

But the new guidelines only require sex scenes to follow the storyline and not be high in impact.

"Higher than what?" says Ms Phillips.

"As we've seen over the years, what one person thinks is high is not necessarily what the program manager for Channel 10 thinks."

That is a reference to a long running stoush over the Channel 10 show, Californication.

The Australian Communications and Media Authority has upheld a complaint by Family Voice about one of the show's sex scenes.

"Absolute ... it was a threesome and it was extremely explicit," she says.

"I won't go into details, but if it wasn't for that word 'discreetly' in the guidelines, that complaint wouldn't have been upheld."

But media commentator Sue Turnbull from La Trobe University in Melbourne says the group is overreacting.

"If this particular group don't know what real pornography looks like, then maybe they should see some, so that they can actually make the kinds of distinctions that the people that are doing this classification make every day," she said.

Family Voice Australia is also worried about new guidelines for the new digital channels the networks have launched.

While the core channels will still be required to show only G-rated programs in the hours before and after school on weekdays and in the mornings at weekends, the new channels will not be.

"The new digital televisions provide all sorts of capacities for parents to lock their children out," says Ms Turnbull.

"In fact, if this family organisation is being really sensible, what it should be doing is talking about sex education, media education, media literacy.

"And what parents can actually do in the home as responsible parenting just to ensure that their kids know what's out there, know how to cope with it and are not traumatised by something that they might come across that can just kind of switch on past it and go 'yeah, I don't want to look at that'."