About 500 workers at Pakistan's largest, state-owned telephone company have been detained after they went on strike to thwart a privatisation move, a union leader said yesterday.

Shahid Ayub said the industrial action, launched on Sunday to head off a plan to sell a 26 per cent stake in Pakistan Telecommunication Company Ltd (PTCL) had disrupted more than 200,000 phone lines.

But a top company executive rejected that claim, saying only 500 lines were disrupted by a fire late on Sunday and that most workers turned up for work yesterday.

Ayub said thousands of workers were striking and services were disrupted mainly in the southwestern Baluchistan and the eastern Punjab provinces. He said hundreds of workers staged sit-ins near telephone exchanges in various cities yesterday.

The unions have threatened major disruption of telephone services tomorrow if the share sale, set for June 18, is not scrapped.

Junaid I. Khan, PTCL chief executive, said that telephone facilities were running smoothly, although 500 phone lines were disrupted by a small fire in the eastern city of Lahore. "We suspect the fire is linked to the strike," he said.

"The strike is illegal and disciplinary action will be taken against those participating in it," he said.

Union leader Ayub said that 500 PTCL workers had been arrested in raids across the country.

Authorities have confirmed dozens of arrests, and security forces, including communications engineers, have been deployed at telephone facilities across Pakistan.

The government warned on Sunday that striking workers could be charged under anti-terrorism laws if they "tried to incite violence."

In Lahore, police chief Tariq Saleem said 24 PTCL employees had been detained under the Maintenance of Public Order Act, under which they can be held for 90 days.

Other police officials, speaking on condition of anonymity because they weren't authorised to comment to journalists, said that in all 60 were in custody in Lahore, many of them workers' relatives who were picked up as workers themselves were not present when police conducted raids on their homes.

Sabir Butt from the PTCL Employees Action Committee accused police of intimidating and harassing workers and their families.

PTCL has defended the proposed sale, saying it would attract capital, new technology and lead to better service.

The company also says it will protect the interests of workers and has recently provided them a hefty pay rise.

Union leaders, however, claim thousands of workers will lose their jobs, and question the need for the privatisation as PTCL currently makes a profit.