The two Chinese men were under the protection of the UN High Commissioner for Refugees (UNHCR), said Francois Lasalle, spokesman for Canada's foreign ministry.
"We have expressed serious concerns with both countries, including our deep disappointment that the individuals were sent by Thai authorities back to China despite being in possession of UNHCR protection documents," Lasalle said.
The Thai junta knew that two Chinese men it detained were refugees awaiting resettlement in Canada but still deported them to China, according to a United Nations letter seen by Reuters.
The letter, reported on by Reuters on Monday contradicts Thai Prime Minister Prayuth Chan-ocha's statement last month that Thailand "did not know" that the men were under UNHCR protection.
Military-ruled Thailand arrested the men, Jiang Yefei and Dong Guangping, on Oct. 28 and deported them at Beijing's request in mid-November.
In the letter, dated Nov. 16, the UNHCR raised its objections to the deportations and reminded the Thai Foreign Ministry that it had informed the government in writing on Nov 10 that the men were refugees and had been accepted for rapid resettlement by Canada.