a person or group of people who have a disagreement with a company, usually the one where they work, and who walk around in a line outside the place of business to tell other people not to enter until the problem is solved:

also picket line a group of people who stand outside an organization's building holding signs to protest against something. The people who protest are often employees who disagree with the management:

UK a single person in a picket line:

to show an organization that you are not satisfied with them by standing outside their building and trying to prevent people from entering and doing business with them :