Police authorities in Pakistan announced arresting 150 hardline activists on Wednesday. They were taken trying to gather for a protest in support of a country’s strict blasphemy law on the anniversary of a provincial governor’s assassination over his call to reform the statute.

Punjab Governor Salman Taseer was gunned down by his bodyguard Mumtaz Qadri six years ago for championing the case of a Christian woman who was sentenced to death under the blasphemy law, which he said needed to be reformed.

Lahore Deputy Inspector General of Police Haider Ashraf said the arrested activists belonged to Tehreek-i-Labaik Ya Rasool Allah, a coalition of extremist groups who were planning to attack people staging a commemoration the anniversary of the governor’s killing. Tehreek-i-Labaik Ya Rasool Allah could not be reached for comment.

Security was tight in the eastern city of Lahore throughout the day. Police locked down many parts of Lahore to prevent demonstrators from gathering, causing massive traffic jams.

Last February, Pakistan executed Taseer’s killer, but tens of thousands of supporters turned up at his funeral and hailed him as a hero of Islam.

Those arrested were booked for disrupting law and order and assaulting police. The head of the Labaik group, Maulana Khadim Hussain Rizvi, was also among those detained.