Picketing is a form of protest in which people (called picketers) congregate outside a place of work or location where an event is taking place. Often, this is done in an attempt to dissuade others from going in (“crossing the picket line”), but it can also be done to draw public attention to a cause.

The unionized workers who are involved in picketing are called pickets.

They involve in picketing mainly because they have some disagreements with the employer.

Picketing is lawful only if it approved by a majority vote in the union. Also workers in a picket line need to be peaceful and it is unlawful for them to force people to not enter the premises of the employer. The main purpose of picketing is to pressurize the employer to agree to the demands of the union workers or to bring to the notice of the employer the grievances of the union workers.

Picketing is allowed only to those employees who work at the workplace outside which they picket. For example a business may operate from various locations however workers can picket only outside the location where they work or where their unions are certified. They cannot picket outside other locations of business of the employer.

There are three types of picketing:

1) Informational Picketing: When pickets inform people about the concern of their union to the public.

2) Mass Picketing: When pickets try to gather as many people as possible in the picket line in order to show the employer that their cause is supported by a large majority of people.

3) Secondary Picketing: When pickets try to stop suppliers of the employer like lorry drivers etc from delivering supplies to the employer.

4) Flying Picketing: When workers involved in an industrial action move from one workplace of the employer to another to picket them. This type of picketing is unlawful.

Source wikipedia