The Election Commission (EC) has warned voters against taking photos of their marked ballots for display on social networks.
In a Dos and Don'ts statement on the EC website, the watchdog said taking photos of marked ballots would be a violation of the election law and punishable with a year in jail.
The EC vowed to take action against a voter who took a photo of a marked ballot during advance voting by Thai expats.
The statement also warned against any action that would damage the ballots.
In past elections, several voters were arrested for damaging their ballots, as they misunderstood that they had to tear the number to mark it.