NHK has learned that Japanese motorcycle makers Honda Motor and Suzuki Motor are considering ending production of small bikes in Japan.
That has been prompted by the impending introduction of stricter emissions standards and a shrinking domestic market.
Sources say the plans apply to motorcycles with an engine displacement of 50 cubic centimeters or less.
Only Honda and Suzuki are making such models in Japan.
Emissions regulations covering this class of motorbike are set to be strengthened in November next year.
After that, manufacturers will have to modify their existing engines to continue production.
The sources say the companies believe it would be technologically difficult to develop small motorcycles that meet the new standards and that new investment would not pay off given the shrinking market.
Ending production would affect another Japanese motorcycle maker, Yamaha which buys two models from Honda and sells them under its own brand. Yamaha also imports one model produced in Taiwan, but has not yet said what it will do to adapt to the new regulations.