The Thai army has sent four companies of soldiers to assist police officers at the protests, an army commander said on Tuesday.
The area around the government building has been occupied since last week by anti-government demonstrators.
Samak is refusing to stand down and his supporters have demonstrated their backing on the streets and in parliament.
A coalition of 43 unions said on Monday that workers will on Wednesday cut off water, electricity and phone services at government offices and disrupt flights of the national airline in support of the anti-government protesters.
“The government has beaten protesters, and that justifies our retaliating by stopping water, telephone service and electricity to some government agencies,” Sawit Kaewwan, secretary-general of the State Enterprise Workers Relations Confederation, or SERC, told a news conference.
Samak's government has been under siege for nearly a week, after a movement calling itself the People's Alliance for Democracy (PAD) stormed the prime minister's compound and forced the closure of airports and railways in other parts of the country.
Anti-government protesters and opposition leaders have been demanding that Samak dissolve parliament and call new elections.
But his supporters staged a counter attack on Sunday, with more than 1,000 gathering at the gates of parliament to show solidarity with a government they say was democratically elected by the people.
Smaller political parties who help make up the ruling coalition that controls more than two-thirds of parliament's more powerful lower house, have also vowed to stand by Samak.
|Samak has refused to step down [AFP]
Analysts say Thailand's economy has never really recovered since the coup that ousted Thaksin Shinawatra as prime minister nearly two years ago and some had hoped that the country was finally getting on track to recovery.
But the latest standoff between protesters and the government may be threatening that recovery.
With airports in popular holiday areas such as Phuket and Krabi shut down by protesters and threats of further enforced closures, tourists may begin staying away.
The PAD claims the government is a puppet of Thaksin who was ousted in a military coup amid allegations of corruption.
The PAD's anti-Thaksin demonstrations in 2006 had helped to trigger the coup.
Now it wants to topple this government as well because it says the government is attempting to amend the constitution to suit itself.
"We hope that by what we're doing will teach the politicians a lesson that just because they have the majority vote, doesn't mean they can do whatever they want," Sondhi Limthongul, an anti-government leader, said.
The group says that Western-style democracy of one-man, one-vote, gives too much weight to Thailand's rural majority, whom it considers susceptible to vote-buying that breeds corruption.
It wants 70 per cent of parliament appointed and only 30 per cent elected, a move detractors say is undemocratic.
Supporters of the government blame the PAD for destabilising the country.
"The PAD were the ones who invited the military to illegally take control of our country. We don't trust the PAD since all their actions past and present lead our country backward," Somyot Preuksakasemsuk, a government supporter, said.
The influential army commander, General Anupong Paochinda, has vowed that the military will not stage a coup.
The prime minister himself has refused to stand down and give in to opponents he says only reflect a minority in the country.
At a special joint parliamentary sitting of MPs and senators to discuss the crisis on Sunday, a number of politicians called for Samak to step down.
But Samak has said he will not let protesters force his hand.
"I am sure that I love this country as much as anybody," he said. "But I love democracy much more, more than anyone who told me to resign."
Shortly after the end of the debate in the early hours of Monday, a small explosion at a police booth near where there have been anti-governments protests damaged windows, but caused no casualties. No one claimed responsibility for the blast.