The new law will ban most "psychoactive drugs" during this parliament, putting an end to the sale of legal highs common at parties and festivals, such as nitrous oxide – also known as laughing gas or, as some newspapers prefer it, "hippy crack".

Stephen Reid, the founder and director of a group called the Psychedelic Society, has arranged the mass nitrous inhalation – which already has hundreds of attendees on Facebook – to force a discussion on the legality of drugs.

"You may not want to take nitrous oxide but it should be up to an individual to decide whether or not to use it," said Reid. "Plus there have been so many artists over the years mentioning psychedelics – it's certainly embedded into our culture."

The protest will involve the participants filling up colourful balloons with laughing gas and simultaneously inhaling them as one outside of the Palace of Westminster.

The participants have chosen nitrous oxide because "it's legal, but it will be illegal if this law is passed", said Reid. "It's also much more short-acting than [legal hallucinogen] 1p LSD ... so that makes it more suitable for a stunt like this. Also the spectacle of it is more interesting – there will be so many balloons."