Thailand's public sector unions met on Friday to discuss possible strike action in support of a weekend anti-government rally triggered by the death of a protester in a grenade blast.
The umbrella group of all state labour unions, which include utilities, train, plane and port workers as members, is due to announce its decision about Sunday's demonstration around midday (0500 GMT), its leaders said.
"We will come up with measures to encourage as many state workers as possible to go on strike and join our rally," Sirichai Maingam, union chief at state power producer EGAT, told reporters before the meeting.
In August, a partial strike by the unions in support of a long-running anti-government street movement caused havoc on the roads and railways, delaying shipments of commodities ranging from crude oil to rubber.
The People's Alliance for Democracy (PAD) accused the government of having a hand in Thursday's firing of a grenade into the prime minister's official compound, which PAD supporters have occupied since August.
Besides the dead man, 23 people were hurt in the blast, the most serious in a series of small attacks against the PAD sit-in in the last few weeks. Prime Minister Somchai Wongsawat has denied any responsibility.
There are fears the PAD will try to blockade parliament on Sunday with thousands of supporters ahead of a special session on Monday relating to next month's regional summit to be hosted by Thailand in the northern city of Chiang Mai.
The last time the PAD employed such a tactic, on October 7, two people were killed and hundreds injured in running battles with riot police -- the worst street violence in the Thai capital since the army opened fire on democracy protesters in 1992.
House leaders said they were not prepared to move Monday's session to a new venue, setting up a potentially serious confrontation.
"We are talking about the pride and dignity of parliament and the country," Deputy House Speaker Apiwan Wiriyachai told a Bangkok radio station.
The PAD, a loose coalition of royalist businessmen and academics who accuse the government of being a puppet of ousted leader Thaksin Shinawatra, have managed to muster crowds in the tens of thousands this year.
However, in the last few weeks their numbers at Government House have been dwindling, largely through fatigue and the absence of anything inflammatory from the elected administration, which is operating out of temporary offices at an old airport.
Even if Monday passes off without incident, tensions are likely to remain high, with Thaksin -- now in exile having skipped bail in a corruption case -- set to address a mass rally of supporters around Dec 13.
The army has said repeatedly that another coup would not solve Thailand's fundamental political problems, and analysts say it is unlikely to change that view unless major street violence breaks out.