The Election Commission (EC) said about 1,500 ballots cast in New Zealand were ruled invalid because they arrived at constituencies after polls closed. The EC said it would find those responsible on Monday.
EC secretary-general Jarungvith Phumma said on Sunday evening that the ballot papers were from advance voting in New Zealand and they did not arrive in time.
"The law requires all ballots from advance voting must be accepted at constituencies before polling stations closed at 5pm so that they could be mixed with other ballots and would not indicate for which parties they had voted. Failing to meet the deadline, the law considers them as invalid," Mr Jarungvith said.
"I have learned that a flight from New Zealand had to fly to another country before arriving in Thailand and it might have been delayed."
The diplomatic mail sack containing the ballots was set to leave New Zealand on March 18 and arrive in Thailand on March 22. But it landed on the morning of March 24. The EC would meet on Monday to determine if anyone should be held responsible, the EC secretary-general said.
Of the roughly 1,500 ballot papers from New Zealand, about four were for each of 350 constituencies, he said.
