Stand Up To Racism protesters are planning a vigil outside a London police station on Monday after a black man died following a police chase.
Campaigners say they are "enormously concerned and angered" over the death of Rashan Charles over the weekend.
Unverified footage on social media appeared to show at least one police officer attempting to restrain Mr Charles on the floor of a shop, in Kingsland Road, east London, at 1.45am on Saturday.
Metropolitan Police said the 20-year-old was seen "trying to swallow an object" and that an officer "sought to prevent the man from harming himself".
Mr Charles was later pronounced dead in hospital.
The police watchdog is investigating.