Critics accuse Samak of being a proxy of Thaksin Shinawatra, the former prime minister, who was removed from power in a 2006 coup amid allegations of corruption and abuse of power.
But the prime minister has reamined defiant, telling Thai senators on Monday not to "mess with someone like Samak" during the opening round of the censure brought by the opposition in the senate.
"Don't try to slander and accuse me like you did Thaksin, who has been tarnished by accusations," he said.
|Samak is in no mood to quit [AFP]
"You think I'll consider myself incapable and quit? That is insane."
The prime minister has said he will consider stepping down if the no-confidence vote succeeds.
But analysts say his opponents are unlikely to muster enough votes in parliament on Tuesday given the size of Samak's coalition majority in the lower house.
Samak's six-party government coalition, which is led by his People's Power party, controls about two-thirds of the 480 seats in the lower house and his partners will have to desert him for the vote to succeed.
"The stability of government is still good. The coalition partners will not be swayed by the debate of the opposition. They will vote to retain Samak as prime minister," Natawut Saikau, the government deputy spokesman, told the Associated Press news agency.
Protester numbers have dwindled from the tens of thousands of people on the streets of Bangkok over the weekend, but Samak's critics say they will not be satisfied until the entire government steps down.