The World Trade Organization has rejected a US appeal of its decision that country-of-origin labelling (COOL) on meat unfairly discriminates against imports into the country.

The final ruling launches a WTO process to determine the level of retaliatory tariffs Canada and Mexico can impose on the US. Washington will have to revise or repeal its COOL regulations in order to avoid such sanctions.

The WTO launched a probe into the US COOL rules following a request from Canada, which argued Washington was implementing "unfair trade practises".

According to the WTO, the COOL labelling requirements breach the Technical Barriers to Trade (TBT) agreement by "according less favourable treatment to imported Canadian cattle and hogs than to like domestic cattle and hogs".