Thousands of Sikhs are expected to take part in a march and rally in central London on Sunday.
The march is held every year
The Remembrance March will commemorate the 22nd anniversary of the Indian army's attack on the Golden Temple in Amritsar - the holiest Sikh shrine.
Sikhs of all ages are expected to attend the march, from Hyde Park to Trafalgar Square.
At the rally, Sikhs, who make up 3% of India's population, will be calling for the right to self-determination.
On 6 June, 1984, Indian Prime Minister Indira Gandhi sent the army into the temple to flush out militants.
There has never been agreement on the numbers killed, but Sikhs say thousands were massacred by Indian troops, many of them innocent bystanders.
The military action 21 years ago led to Mrs Gandhi's assassination later that year by her Sikh bodyguards.
That in turn triggered a wave of anti-Sikh rioting which left nearly 3,000 dead.