Thailand's Constitutional Court will decide on Friday whether government plans to amend the constitution are legal.
The current constitution was drawn up by the military, which deposed former Prime Minister Thaksin Shinawatra, and the party of current prime minister Yingluck Shinawatra -- Thaksin's sister -- says the amendments are needed to bring more democracy to Thailand.
However, opposition Democrats say the changes would threaten the role of the revered monarchy and allow the exiled Thaksin Shinawatra back into the country without doing jail time for a conviction on corruption charges.
A ruling either way could spark a return to street violence that paralyzed Bangkok in April and May of 2010.