PORTLAND, OR (KPTV) – Portland police say they're bracing for a big showing at May Day marches in the downtown core Tuesday.The annual May Day rally and march is expected to begin at 4:30 p.m. While it's a permitted event celebrating workers' rights, police said they have concerns about unaffiliated groups attempting to disrupt the event and engage in illegal behavior.”Available information suggests that there will be other nonaffiliated groups that may engage in direct action both before and after the permitted May Day event,” a police spokesman said in a statement Monday.The police bureau said those who “willingly commit illegal acts must be aware of the consequences,” which include arrest.Police said downtown businesses should be aware of the event and prepare for possible traffic disruptions.The permitted May Day celebration starts at 3:30 p.m. with a rally in the South Park Blocks. The march is scheduled for 4:30 p.m. until 6:30 p.m.A post on the Occupy Portland website, however, lists “unpermitted” events, including a “roaming dance party” starting in the South Park Blocks at 6 p.m.Copyright 2012 KPTV (Meredith Corporation.) All rights reserved.