An executive from Theppandungporn Coconut company confirmed the sales performance news adding it was auditing plantations to show animals were not used.
The animal rights group People for Ethical Treatment of Animals (PETA) released a report alleging that coconuts in Thailand are picked by abused monkeys.
The fallout after the PETA’s report included British retailers removing Thai coconut products from their shelves earlier this month.
"We saw sales fall 20 to 30 percent (from last year) after the news," said Aphisak Theppadungporn, Managing Director of Theppadungporn Coconut Co. Ltd.
The company is one of Thailand's biggest producers and exporters which makes Chaokoh coconut milk.
The fiancée of British Prime Minister Boris Johnson has chimed in the monkey labor conversation.
Carrie Symonds had welcomed pledges to stop selling coconut products that use monkey labor and encouraged others to follow suit.
PETA has rejected the Thai government's claim that use of monkeys was almost "non-existent". Its report said the majority of Thai coconuts were harvested by monkeys caught from the wild.
Aphisak said evidence and documents were being prepared for customers in its main markets, and for PETA, to show monkeys were not involved in Theppadungporn Coconut products.