Prime Minister Scott Morrison has described the Sydney Opera House as a "big billboard" and says he'd happily advertise events on the Harbour Bridge too.

Mr Morrison's comments came after NSW Premier Gladys Berejiklian on Friday ordered Opera House management to allow Racing NSW to advertise the up-coming Everest Cup horse race on the sails of the iconic venue.

"This is one of the biggest events of the year why not put it on the biggest billboard Sydney has," the prime minister told reporters in regional NSW on Sunday.

"These events generate massive economic opportunities for the state and the city.

"I'd put the Bathurst 1000 (car race) on the Harbour Bridge if I thought it was going to get more people there."

The PM - speaking in Blayney just 30 kilometres southwest of Bathurst - said promoting the Everest Cup on the Opera House was "just common sense".

"I don't know why people are getting so precious about it," he said.

"Frankly I thought it was a bit of a no-brainer."

Premier Gladys Berejiklian on Sunday denied she caved into bullying from broadcaster Alan Jones when she intervened to allow the horse racing advertising to be projected onto the sails.

Jones on Friday harassed Opera House chief executive Louise Herron who'd ruled against allowing words or branding to be projected onto the venue because "it's not a billboard".

Within hours the premier had intervened to ensure Racing NSW could promote Tuesday night's barrier draw for the Everest Cup using the Opera House.

"There'll be no logos or names - the only words on there are the words on the trophy itself," Ms Berejiklian told reporters on Sunday.

"That is consistent with what's happened in the past - whether it's other sporting events or opportunities or other artistic expressions."

The Liberal leader said her intervention followed "weeks and weeks of negotiation".

"It is happening on Tuesday and that was the timeliness of the issue," she said.

The premier argued the display to be shown was "much toned down to what the government was first presented with".

Anti-gambling activist Tim Costello says Jones's "nasty hectoring" of Ms Herron and his "sheer brutality" shouldn't surprise anyone.

"He has long been a promoter of the gambling industry and also has commercial interests in racing," Mr Costello wrote in the Guardian on Sunday.

The Guardian also reports the United Nations body that declares world heritage sites is "looking into" the Racing NSW promotion.

But the premier insists the Opera House's status is not at risk.

"I'm absolutely confident the Sydney Opera House will continue to be the icon that it is globally and for us locally," she said.

A petition to "Defend Our Opera House: Support Louise Herron" on change.org has been backed by 45,000 people.

Mr Morrison, as Tourism Australia director in the mid-2000s, oversaw the controversial ad campaign featuring model Lara Bingle asking would-be visitors "Where the bloody hell are you?"