The letter by a wide array of China experts from around the world is addressed to Chinese President Xi Jinping. It says the arrests of the two Canadians sends a worrisome signal to those who work in policy and research in China.
China detained former Canadian diplomat Michael Kovrig and Canadian entrepreneur Michael Spavor on Dec. 10 in an apparent attempt to pressure Canada to release Chinese executive Meng Wanzhou, who was arrested Dec. 1 at the request of U.S. authorities.
Meng is the chief financial officer of the Chinese tech giant Huawei and the daughter of its founder. The U.S. wants her extradited to face charges that she committed fraud by misleading banks about Huawei's business dealings in Iran.
The letter, released Monday, notes Kovrig is a former diplomat who was working as an expert on Asia for the International Crisis Group think tank. It notes that Spavor devoted his time to building relationships between North Korea and China, Canada and United States.
It praises Kovrig and Spavor as bridge-builders between China and the world and said their arrests make writers "more cautious" about travelling to China.
"Meetings and exchanges are the foundation of serious research and diplomacy around the world, including for Chinese scholars and diplomats," the letter says. "Kovrig and Spavor's detentions send a message that this kind of constructive work is unwelcome and even risky in China."
The letter said the arrests will lead to "less dialogue and greater distrust, and undermine efforts to manage disagreements and identify common ground. Both China and the rest of the world will be worse off as a result."
More than 20 diplomats from seven countries and more than 100 scholars and academics from 19 countries signed.
Guy Saint-Jacques, a former Canadian ambassador to China, signed the letter and noted it comes as Canada is working to rally international support for the case.
"It will be noticed in Beijing and I hope that it will make clear for them that the arrests of Kovrig and Spavor are not only a China-Canada problem but it's also having an impact on the image of and reputation of China," Saint-Jacques said. "It's an impressive list."
The signatories include former British Foreign Secretary Malcolm Rifkind, former Australian Foreign Minister Gareth Evans and Chris Patten, former British governor of Hong Kong. Two former U.S. ambassadors to China, Gary Locke and Winston Lord, also signed.
David Mulroney, another former Canadian ambassador to China, said the letter is significant because it shows the international breadth of support for the two men.
"This isn't simply a Canada-China dispute," Mulroney said. "A lot of serious people, including many who have spent years working in China, are worried about how it is closing itself off, and punishing those who seek to understand and interpret it for others."
Canadian Prime Minister Justin Trudeau said he encourages friends and allies around the world to point out that all countries should stand up for the rule of law.