More than 2,000 police are set to be deployed around the court building in Bangkok, with a force of 13,000 troops and riot police on standby in case of trouble, officials said.
In addition, the Thai information ministry said a dozen pro-Thaksin websites have been blocked amid concerns that they may encourage people to protest on the streets.
Thai Rak Thai - accused of financing obscure parties to run against it to get around rules requiring a minimum voter turnout in constituencies where single candidates run unopposed
Democrat Party - accused of conniving with smaller parties to lure Thai Rak Thai into illegally funding them
The ministry said the block will remain in place until the verdict is out.
Military officials added that mobile phone signals would be turned off during the verdict to allay fears of possible bombings.
"We also have an evacuation plan for the judges and court officials in the event that their security is threatened,'' said Colonel Sansern Chaenkamnerd, a spokesman for the military's Council for National Security.
As part of that plan police boats have been positioned along the Chaophraya River near court building, should the nine judges have to be quickly evacuated following their ruling.
Reports said the authorities had also set up checkpoints on highways heading into the Thai capital to prevent thousands of villagers from entering the city to protest the possible dissolution of Thai Rak Thai.
Thaksin's former party still has strong support in Thailand's rural northeast.
Asked about the checkpoints Sansern said they were "there to make sure people don't carry weapons" into the city.
|The court verdicts will be closely |
followed across Thailand [Reuters]
If the tribunal finds either or both parties guilty they could be dissolved, or their executives barred from public office for five years, or both.
The leaders of both parties have publicly promised to accept the court's ruling, although some senior members of Thai Rak Thai had earlier threatened to stage mass protests if their party was disbanded.
Observers say the generals behind last year's coup are hoping the tribunal's verdict will bar Thaksin from returning to politics.
They say that if Thai Rak Thai is not disbanded, the military's justification for ousting the former prime minister on charges of abuse of power and corruption would be undermined.
Thaksin was ousted in a bloodless military coup last September after months of street protests and flawed elections.
Now living abroad, he and his family are under investigation for alleged corruption and other offences.
Last week the Thai king warned the judges in the case that whichever verdict was reached the security of the country could be at risk.
In a televised address, King Bhumibol Adulyadej, 79, urged the judges to make a clear decision, but said that either way they would be criticised.
Thailand's widely-revered king, the world's longest-reigning monarch, rarely intervenes in politics.