The authority have also sent a list of more than 1,500 Urdu and English words that are to be blocked. The order was also in an attempt to block spam messages, said Rehman.
Reports reveal that many of the words that are to be blocked are sexually explicit or swear words. The list also included words like idiot and fart.
Words like tampon, Jesus Christ, headlights also raised concern over religious freedom and practicality. Any such words would become a part of a spam message.
The letter dated Nov 14 asked cell phone companies to implement the order within seven days.
"It's a big issue , so it is being examined carefully from all points of view," said Rahman adding that her company was thinking on how to go forward on the issue.
The letter also said that the order under 1996 law that prevented people from sending information through the telecommunications system that is "false, fabricated, indecent or obscene" was legal and further stated that free speech could be restricted "in the interest of the glory of Islam".
Pakistan, earlier under pressure from Islamists, had banned pornographic websites and the ones that are anti-Islamic.