The Rowlatt Act, an arbitrary law allowed the British government to imprison people without due trial.
Example:
The Rowlatt Act came into effect on 10 March 1919. In Punjab, protests against this act continued quite actively and on April 10, two leaders of the movement, Dr. Satya Pal and Dr. Saifuddin Kitchlew were arrested. To protest their arrests, a public meeting was held on 13 April at Jallianwala Bagh in Amritsar. General Dyer entered the park with his troops. They closed the only exit and without giving any warning General Dyer ordered the troops to fire. Several hundreds of people died in this gun fire and many more were wounded including women and children.