Just to add a bit more information. That plate is welded to the end of the pin that the arms rotate on. The pin goes through a hole in the casting of the brake case and then sits in a blind hole that is counterbored into the reduction gear case. This latter hole is a tight fit with the pin. So as the former poster suggested rotating the pin by using the tab will help break it loose, especially if it has been in there for a while.
One piece of advice, be sure to reinstall the bolt that secures that tab in place, possibly even with Loctite. If the pin is not secured and backs out under use the consequences are very expensive, don't ask how I know that.