Thousands of people have been invited to the event, at Woodhouse Moor at Hyde Park on Sunday, May 25, via Facebook, the social networking internet site.

Police have since contacted the organisers of the event, believed to be students at Leeds Met University. A recent water fight, organised using Facebook, led to widespread damage to Mandela Gardens in Leeds city centre.

Police are trying to discourage people from organising large events without a licence.

A police spokesman said: "We have contacted the alleged organiser regarding this event and advised him to cancel it. We will be monitoring the situation to ensure that it does not take place.

"West Yorkshire Police will work with our partners in the council to close down any un-licensed events that take place in the region's public places.

Any such events, especially those potentially involving large numbers of people must be given the proper licence by the council in advance. While such an event may seem like a bit of fun, it is easy to see how a mass pillow fight could get out of hand and potentially cause our officers a significant amount of work."

Last night the Facebook page promoting the pillow fight said it had been cancelled, although a note posted by one organiser said: "If by pure co-incidence hundreds of people happen to turn up at the same time in the same place and engage in pillow fighting activities, this is totally unavoidable and the creators of this event cannot be held responsible."

The Yorkshire Post emailed two of the organisers but they did not respond.