President Pervez Musharraf has signed into immediate effect measures to increase control over the media.
Gen Musharraf is facing an unprecedented challenge to his rule
Current regulations related to television have been extended to the internet and mobile phones.
Some regulations on who is allowed to be licensed to broadcast in Pakistan have been extended to cover "any foreign non-governmental organisation".
Gen Musharraf has been highly critical of the media in recent weeks over its coverage of opposition protests.
Correspondents say Gen Musharraf is facing the most serious challenge to his rule from a coalition of opposition parties and groups.
Their frequent street demonstrations mark the first big protest movement in Pakistan to take place as the country has entered an era of rapidly expanding, live TV news coverage.
The protests were sparked off by Gen Musharraf's suspension of the chief justice of the Supreme Court on 9 March.
Threat to premises
The amended media regulations were changed on Monday because "circumstances exist which render it necessary to take immediate action", a government statement said.
Chief Justice Chaudhry is now the centre of the opposition
Broadcasters and cable distributors who break the rules could have their premises closed down.
Non-print media in Pakistan is regulated by the Pakistan Electronic Media Regulatory Authority (Pemra).
Pemra will now also be able to suspend the licence of an offender.
Talat Hussein, the director of news for one leading station, Aaj TV, told the BBC: "The government is getting frustrated... and the messenger is being killed for the message."
He was critical of Gen Musharraf for pushing through legal amendments at a time when parliament is not in session.
"It's a repressive law and it's very clear that the government does not want any visuals on the TV screens which are against its policies," Mr Hussein said.
Regulations previously only applying to 'direct to home' television services will now apply to 'IPTV, Mobile TV' (video content on the internet and TV on mobile phones).
The new rules also extend the restrictions on foreign broadcasting in Pakistan. Until now there were bans on non-Pakistanis and foreign companies.
The new restrictions now include "any foreign non-governmental organisation". Correspondents say it is not yet clear what this new clause will mean in practice.
Since the current political crisis began in March the media, in particular television, have come under the spotlight.
President Musharraf has openly criticised TV stations for giving airtime to his critics.
On Friday top army commanders said there was a "malicious campaign" against institutions of the state by a small minority of vested interests.
On the same day two private TV channels were prevented from live broadcasting after making alleged criticisms of the army and judiciary.
Gen Musharraf suspended Supreme Court Chief Justice Iftikhar Chaudhry because he said he was guilty of misuse of office.
Judge Chaudhry's supporters say that Gen Musharraf was trying to muzzle the independence of the judiciary in an election year.
Most of Pakistan's legal community came out in open support of the judge. They were soon joined by Pakistan's religious and secular opposition parties.
Many of their protests have resulted in bloodshed.