Thailand's three election commissioners have been jailed for four years for mishandling April's poll.
The Election Commission is seen as pro-Thaksin
Bangkok's Criminal Court found the men guilty of flouting the law by allowing unqualified candidates to stand.
The poll was controversial as it was essentially a one-horse race, due to a boycott by the main opposition. The courts later annulled it.
The verdict was a blow to PM Thaksin Shinawatra, as the Election Commission had been seen as his ally.
The commissioners have been under fire for some time, with many people urging them to quit in time for the next poll, which the king recently confirmed would be held on 15 October.
A lawyer for the men said they would appeal Tuesday's verdict.
The April poll was always going to be controversial, because the main opposition party, the Democrats, decided to boycott the process, leaving Mr Thaksin's Thai Rak Thai as the only major party standing.
There were widespread concerns over the poll's legitimacy, and after a highly unusual intervention from the king, the country's top courts decided to nullify the election and start again.
Amidst all the arguments surrounding this fiasco, there has been one constancy - an almost universal call from the courts, the opposition and the Thai media for the election commissioners to take the blame and resign.
One commissioner quit shortly after the poll was annulled, but the other three have so far steadfastly refused to back down.
Now it appears they may be going by force. On Tuesday they were found guilty of violating election laws and letting unqualified candidates run in some constituencies, especially in the second round of the poll, when there was intense pressure to find alternative candidates to Mr Thaksin's Thai Rak Thai party.
"The election commissioners carried out the elections in an unfair manner," the Criminal Court said in a statement. "They are found guilty... and the court sentences them to four years in prison."
The ruling also means they will not have the right to vote, or conduct any political activities for 10 years.