Activists from Greenpeace climbed Montreal's Olympic tower Thursday morning to show their opposition to the Trans Mountain pipeline.

The activists began climbing the tower around 7 a.m. and after an hour and a half unfurled a banner reading "Stop pipelines. Don't dirty our money."

Earlier this year the federal government agreed to buy the pipeline for $4.5 billion so that oil from Alberta can be transported to the pacific coast and sent to refineries.

Spokesperson Loujain Kurdi called on Prime Minister Justin Trudeau to reverse that decision.

"Climate leaders do not build pipelines and we are urging him not to invest this sum. Furthermore his own youth council two days ago also asked him to hold the investment as they were deeply disappointed by his decision," said Kurdi.

Montreal police observed the climbers from the ground and arrested all three, along with four other protesters, for mischief once they descended.

During the protest police prevented people from getting close to the stadium, and the funicular which runs up the tower was halted.