From Longman Dictionary of Contemporary Englishpicket lineˈpicket ˌline noun [countable] a group of people who stand outside a factory and try to prevent people from going in or coming out during a strikeon a picket line So far, there has been very little violence on the picket line. Very few workers were willing to cross the picket line.
Examples from the Corpus
picket line• They shouted the news that the Confederates were making an attack on the picket line with a heavy force..• Things are quiet on the picket line on this Sunday afternoon.• Hundreds of trade unionists came day after day to support the Grunwick strikers on the picket line.• Now get this: the other workers respected the picket line.• The picket line was supplemented by daily long-range air patrols by naval aircraft.on a picket line• Paisley stood on a picket line outside the Ballylumford power station in Larne and tried to persuade workers not to go in. 