Accusations are flying about alleged spy cameras at Beirut airport
Lebanon's government has declared an extensive telecommunications network run by the powerful Shia opposition movement, Hezbollah, illegal.
The Western-backed government said it would close down the system, which it called a threat to state security.
Tension is also high after the chief of security at Beirut airport was removed for alleged Hezbollah sympathies.
Last week the authorities accused Hezbollah of installing spy cameras at the airport - allegations it denies.
The Lebanese government announced a series of security decisions after a marathon cabinet session which lasted until after 0400 (0100 GMT) on Tuesday.
The BBC's Jim Muir in Beirut says government-opposition tension and invective is already extremely high and the latest decisions are bound to be seen as confrontational by the opposition.
The political crisis has left Lebanon without a president since November 2007; parliament has aborted 18 attempts to elect a head of state since then.
Hezbollah is reported to operate an extensive fixed-line telecommunications network covering its strongholds of south and east Lebanon, and the southern suburbs of Beirut.
The Syrian- and Iranian-backed group has made clear that it regards the private network as an integral part of its defensive measures against Israel.
The political and guerrilla organisation says the system played a key role in its war with Israel in 2006.
The government ordered the commander of security at Beirut international airport, Brig Gen Wafiq Shuqeir, to return to the Army Command.
It suspects him of sympathising with Hezbollah, and accused him of failing to deal with a secret camera allegedly set up by Hezbollah in a container overlooking the main runway, to monitor the movement of aircraft and VIPs.
The opposition is supporting a general strike on Wednesday by workers demanding higher wages.
There are fears that the tensions could lead to a new round of street clashes, our correspondent says.