South Korea’s most-polluting companies have made 475 billion won ($357 million) from selling unused carbon emissions permits in the first eight years of the nation’s program, according to an activist group.

The 10 biggest emitters sold almost 22 million tons of excess credits from 2015 through 2022, according to Plan 1.5, a Seoul-based climate advocacy group. The nation’s cap-and-trade system, which covers almost 700 companies, had a surplus of 39.2 million tons in 2021 and 2022 combined, the group said in an analysis. That’s equivalent to about 6% of Korea’s total emissions in 2022.

South Korea was one of the first nations in Asia to start an emissions-trading system, but it has fallen short of encouraging industrial polluters to reduce pollution because too many allocations were supplied, most of them for free. The analysis puts further pressure on the government to improve the program, which is a central pillar in the nation’s pledge to cut the release of greenhouse gases by 40% from 2018 levels by 2030.