An online protest this morning was building aimed at Facebook’s new data center in Oregon. The issue? How it intends to power its social network of 400 million strong: with “dirty coal.”

Naturally, environmental activists are crying foul. So far, Change.org has rounded up 3,000 online signatures (as of this writing), with a goal of 5,000, to force Facebook to go green.

There are already several protests sites on Facebook itself, with the biggest nearing 4,000 members. It questions Facebook’s commitment to a low-carbon footprint, saying:

The center will be designed to conserve energy, according to Facebook, but this does not change the fact that coal-fired electricity is the dirtiest way to post a photo on your profile (or do anything else online.)

What is going on, Facebook?

Here’s an example of having your megaphone turned against you. Facebook has already had to cave in to users’ wrath in instances when users privacy was threatened. It remains to be seen – and no doubt Facebook will be watching closely – whether the protest gains enough traction to force any concessions from Facebook’s core of eco-activists. As the ranks of protesters build, it shines a halogen light on Facebook’s green ways, an issue dear to social networkers. Meanwhile, Microsoft and Google are pioneering low-carbon data center design.

In the rhetoric of Facebook protesters, sharing a photo on Facebook = polluting the planet. Would that make Buzz the green choice?