The decision by ratings agency Moody's to downgrade Thailand's outlook was premature as trade talks with the United States have not concluded, the government said on Wednesday.
The economy is still growing and the government plans to implement economic stimulus to boost growth in the second half of the year, it said in a statement.
On Tuesday, Moody's changed Thailand's rating outlook to negative from stable, citing risks that Thailand's economic and fiscal position could weaken further.
US tariffs were likely to weigh significantly on global trade and economic growth, and that would affect Thailand, the ratings agency said.
There remains significant uncertainty as to whether the US will implement additional tariffs on Thailand and other countries after a 90-day pause on implementing the levies ends in July, it said.
"This shock exacerbates Thailand's already sluggish economic recovery post-coronavirus-pandemic, and risk aggravating the trend decline in the country's potential growth," Moody's said.