Update 5:40 p.m.  Action hasn't actually ended conflict-free. Arrests continue now, reports The Atlantic Wire's Adam Martin from Grand Central. Police apparently detained one woman, and now the stairway down to the dining concourse where police took this woman has been closed off. The group responded by chanting "the whole world is watching."

Occupy Wall Street protesters have ended their day of marching against the National Defense Authorization Act at Grand Central station in New York City, where, according to folks on Twitter, police began making a few arrests even before their scheduled 5 p.m. "action." (Watch a video below of what appears to be police dragging a man away from the group.) The group "mic checked" a public statement calling the new act unconstitutional, which they broadcast on their livestream, and which police appear to have allowed happen unhindered. Having been in Grand Central at rush hour, we can safely say they at least have a large audience of people passing through, though how willing commuters will be to deal with the hubub is less than clear... The group seems to have dispersed relatively peacefully though, but not before mic checking, "The cool thing about flash mobs is that they pop up, and then they disappear."