An ad featuring a Hollywood star dressed in a schoolgirl outfit inviting female law students to "network" their way to the top has been slammed as sexist by women lawyers.

The latest edition of student magazine Lex, published by the New Zealand Law Students Association (LSA), shows actress Blake Lively in character as private school girl Serena van der Woodsen from the United States television show Gossip Girl in a provocative pose.

It comes with the tagline: "She didn't become a good lawyer by spending hours in the library . . . She networked her way to the top."

The ad then invites law students to "Join the NZLSA Facebook page. NOW."

But the LSA insists the ad is satirical despite receiving international condemnation on social media.

The advertisement was re-posted on US-based Facebook page "Wipeout Sexism on FB" this week, drawing immediate reaction.

Many asked whether Lively had given her permission for the image to be used, while others slammed New Zealand's attitude to gender equality.

"OMG, I can't believe that's my country, how shameful," Geraint Scott posted.

"I was not aware that see-through shirts and cleavage was the trademark of a good lawyer in New Zealand. Apparently I have a lot to learn about their judicial system," said Majken Aune Olsen.

Professor Margaret Wilson, a former attorney-general and current deputy dean of Waikato law school, told the Waikato Times the ad was "disrespectful of women law students who in my experience work so hard to achieve their law degrees".

Waikato University morals and ethics lecturer Tracey Bowell said the ad was "absolutely" sexist and demeaning towards women.

"I doubt that an image of a male law student would be used in similar fashion," she said.

Hamilton-based Labour MP Sue Moroney was also unimpressed with the advertisement.

"[The LSA] isn't likely to attract many female members with this archaic approach.

"If they are planning to be the student equivalent of the ‘old boys network' then they will become increasingly irrelevant, as there are now more females than males with tertiary qualifications."

Ms Moroney said the association needed to modernise if it wanted to remain relevant.

"Women are bored with being the butt of these ‘old boy' jokes and we don't have to put up with it any more."

Associate Professor of Law Anna Grear said the advertisement was "insulting to the bright young women I have the privilege to teach".

"As an academic responsible for teaching many bright young female law students, I am truly sad to see their efforts as students, their sheer intellectual talent and all their hard work diminished in this way by the very group who should be defending them from the undoubted sexism that still exists in the profession."

NZLSA president Seamus Woods said that, although he was not involved in the ad's design, it was intended to be "eye-catching".

"It was not intended to be taken seriously, and had a target audience of students, which is perhaps a more robust audience than usual.

"The NZLSA believes that it has a strong mandate to represent female law students and that it does so effectively and earnestly."

A 2011 editor of Lex, George McLellan, said the offending advertisement was a piece of satire based on a 2010 advertisement by Lexis Nexis that was criticised at the time for being sexist.

"We always understood the irony behind the advert, we always understood that 75 per cent of law students are women, and we always intended on punishing Lexis [Nexis] for their short-sightedness."

The furore comes as figures from the Household Economic Survey show a huge disparity between what men and women get paid, with 259,500 men and 92,500 women earning $80,000 or more annually.