Hundreds of demonstrators have shone torches on to the Sydney Opera House to protest against controversial advertising for a horse race that has divided the city and exposed the fault lines in Australia’s culture wars.

The protesters, who sought to interfere with the display on the world heritage-listed structure, chanted “Not for sale” and “Whose house? Our house”.

Racing New South Wales, the body behind the promotion, had envisioned Tuesday’s light show as the grand launch of the $13m Everest horse race. Instead, it has faced an intense backlash.

By Tuesday more than a quarter of a million people had signed a petition against the plan, sparked by concern about the commercialisation of the landmark building and the influence of the city’s vocal conservative media.

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In a furious statement on Monday, Michael Lynch, the former head of the Opera House, said: “I find it extraordinary that the state politicians on both sides have somehow decided that this is in the interests of Sydney, New South Wales or Australia to corrupt the way the Opera House works, to corrupt the artistic integrity of the building and to be able to use it in any way a politician wants.

“I would not regard myself as precious or elitist and I just find the lily-livered approach by the politicians on this issue [and] the nexus between the gambling bodies and the politicians seriously disturbing.”

The lord mayor of Sydney, Clover Moore, told the Guardian that the promotion was “blatant commercialisation of Australia’s world heritage-listed Opera House for an industry notorious for damaging gambling and animal cruelty”.

Others, including prominent politicians on the Australian right, dismissed those concerns. The prime minister, Scott Morrison, supported the plan, calling the Opera House “the biggest billboard Sydney has”.