SARNIA, Ont. - A group of demonstrators descended on this border city Saturday to drop their pants and moon the sky to protest a U.S. surveillance balloon that was hovering nearby recently.

Organizers said between 200 and 300 people took part in the mooning protest, although a local Sarnia radio station put the number closer to 100.

"We got a fellow with a loud voice to shout out a countdown . . . everyone lined up and held it for a couple of seconds, pulled up, and that was that," said one organizer, who would only identify himself as Eli.

"People dispersed pretty quickly afterwards."

The balloon, which is shaped like an airplane wing, had until recently been hovering just over Port Huron, Michigan, just across the border.

It carries a $1-million camera that U.S. officials say is sensitive enough to read the name of a ship from about 14 kilometres away.

The balloon has been grounded since last weekend, when its fabric suffered a gash during a major thunderstorm.

Its absence didn't deter the mooners, however.

"If the balloon's sitting on the ground or it's in the sky, the fact is that they're still using it," said Eli.

"It still needs to be said that we don't think it's necessary, that we think it's a potential invasion of privacy and of sovereignty."

Sierra Nevada Corp., which owns the balloon, is testing technology that could eventually be used by the U.S. Homeland Security.Sarnia Mayor Mike Bradley has said he's written Prime Minister Stephen Harper about his concerns over the surveillance balloon.

Eli said the mass mooning is probably the last he'll have to do with the issue.

"The issue's been brought up, and hopefully something's going to be done about it," he said.

It appeared the protest only drew a fraction of the 1,500 people who indicated on social networking site Facebook that they would show up for the protest.