The union expressed concerns about the possible importation of new variants of the virus during the competition.
“We strongly oppose hosting the Olympic Games in Tokyo at a time when people around the world are struggling with the new coronavirus,” the union said in a statement sent to the government.
“It is impossible to hold a safe and secure Olympics during a pandemic,” the document says.
“We cannot deny the danger that new variants of the virus will be brought to Tokyo from all over the world,” the union said.
The announcement comes amid Japan’s struggle to cope with the fourth wave of the virus infection, with a state of emergency declared in some regions, including the capital.