Police on Sunday arrested around 200 people who strapped themselves to the White House fence to protest the proposed Keystone XL oil pipeline.

The protesters were mostly college students who participated in a peaceful march that began at Georgetown University and ended outside the White House.

The marchers chanted “climate justice now” and carried signs such as “don’t tarnish the Earth” in their efforts to convince President Barack Obama to reject the pipeline. They say it will contribute to global warming.

Protesters were passionate but quite orderly. Police were waiting for them with buses and vans to speed the process. The protesters cheered as police warned them that blocking the sidewalk or strapping themselves to the fence would lead to their arrest.

The Keystone XL pipeline has become a central issue for the environmental movement and landowners in a number of states. More than 86,000 people signed a pledge of resistance promising to engage in civil disobedience if a State Department report expected in the coming months points toward approval of the project.

In January, the State Department’s final environmental review of the project concluded that it would not, on its own, have a significant effect on increasing carbon pollution.