ISLAMABAD (Reuters) - Pakistan has authorised its army-run spy agency to tap telephone calls and messages, strengthening its key role in the politics of the nation, as opposition politicians and social media users voiced concerns over potential misuse or privacy violations.

The powerful military, in a country that has been ruled by the army for almost half its independent history, can make or break governments in Pakistan, and the new powers for its Inter-Services Intelligence (ISI) agency raised widespread alarm.

Law Minister Azam Nazeer Tarar told parliament the ministry of information technology and telecommunications was advised of the change in a July 8 notice.

"Anyone who misuses the law will face action," Tarar said on Tuesday, adding that the measure would be restricted to tracking criminal and terrorist activities and the government would ensure it did not infringe on people's lives and privacy.

"The federal government, in the interest of national security and in the apprehension of any offence, is pleased to authorise officers ... to intercept calls and messages or to trace calls through any telecoms system," said the notice, seen by Reuters.

The move was opposed in parliament by the opposition Pakistan Tehreek-e-Insaf party of jailed former Prime Minister Imran Khan.

Khan had previously backed the ISI's surveillance of politicians' telephone calls, or even his own, without legal authorisation.

A party leader, Omar Ayub Khan, said the agency would likely wield its powers even against lawmakers, and vowed that his party would mount a court challenge.

The army's Inter-Services Public Relations Wing declined to comment. The information ministry didn't respond to a request seeking comment on whether the legal authorisation could lead to violation of privacy and misuse for political ends.

"Is what is "legal" also constitutional or right?" Farieha Aziz of rights advocacy group Bolo Bhi asked on X.

(Reporting by Asif Shahzad; Editing by Clarence Fernandez and Bernadette Baum)

By Asif Shahzad