pp. Greeting and shaking hands with workers at the main gate of a manufacturing plant or warehouse, particularly by a politician during an election.
"June 2, 1999 THUNDER BAY ----------- 12:30 PM Thunder Bay New Democrats Rally Patterson Park (May St. and Miles St.) DRYDEN ------ 4:00 PM Plantgating at Weyerhauser Mill""NDP Leader Howard Hampton strengthens NDP support in Northern Ontario on last day before election," Canada NewsWire
The "quote" given above is part of a politician's schedule during an election campaign. This was the only written source I could find for this word, but I've heard it used on radio and television. -Paul