Women began removing their clothes while Premier Pauline Marois was answering a question.
The premier had been asked about a payroll tax and had just uttered the words, "(We're) taking action now," when shouts erupted in the gallery and everyone's eyes, including the premier's, drifted upward.
As the protesters disrobed, they chanted a slogan against the presence of the crucifix in the chamber: "Crucifix, decalisse," they repeated in a crude, sacrilegious Quebecois expression loosely translatable as, "Crucifix, get the hell out of here."
The demonstration was quelled, as numerous security guards pulled a trio of still-half-naked protesters away from the chamber and struggled to dress them.
All three women were swiftly removed from the building, and protesters later said they were warned they could be charged with disturbing the peace and gross indecency.
The whole affair was in reaction to an uneven approach to state secularism which has been called hypocritical by the PQ's detractors.
The PQ values charter would leave the Christian symbol looming above the chamber where Quebec's laws are passed; Christmas trees would remain in public offices; and the giant cross would stay on the public land above Montreal's Mount Royal.
That's because those Christian symbols are part of Quebec's heritage, the PQ says.
However, lower-level employees of the state would be forced to remove their hijabs, turbans, yarmulkes, and larger-than-average Christian necklaces.
The group "Femen Quebec" claimed responsibility for the bare-breasted brouhaha.
On its Facebook page, the group called itself artists and activists fighting for a Quebec identity that takes into account cultural diversity, and the liberation of women.
One protester said the group doesn't have an official position on the PQ's values charter but opposes the plan to favour Christian icons over other ones.
Xenia Chernyshova said in an interview that the cross was the main target of the protest because it has no place in a room where provincial legislation is debated and enacted.
"It's obvious that it's a symbol — a religious symbol — and it's presented like it's more important than any other religious symbol from other religions," said Chernyshova, who was among the three protesters.
"We don't think it has a place there."
The group has also dismissed the idea that the national assembly cross is integral to the Quebecois identity.
It notes the crucifix was only placed there under the Duplessis regime after 1936, as a symbol of the pact between his now-defunct Union Nationale party and the church.
"(This) crucifix stems from the Great Darkness," the group said on Facebook, employing a term commonly used to describe Maurice Duplessis' pre-Quiet Revolution Quebec.
"(It's) a painful memory, especially for women. That renewal of the pact between the church and the state is not at all a heritage worth honouring. No to a government that accepts the presence of religion at its bosom. Yes to state secularism!"
Another protester, Julie-Anne Beaulac, said security had identified the potential demonstrators beforehand but let them sit in the gallery anyway.
"They told us from the beginning that they'd had problems with Femen, that they didn't want us to do anything, but they let us attend," Beaulac said.
"They stayed posted right next to us."
While the group has no official position on the government's proposed charter, for or against, it says the protests in recent weeks show there's room for debate.
The plan is unlikely to pass the legislature in its current form. That means it could either be watered down, or preserved for use in the PQ's next election platform.
As for the idea that Christian icons should get an exemption because they're part of Quebecois history, one protester painted a message on her body: "Heritage (belongs) in the museum."
-With files by Alexander Panetta, Sidhartha Banerjee and Alexandre Robillard
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