“Our production of uranium necessary for military and electric power has dropped from 49% of our consumption to 5%,” said Commerce Secretary Wilbur Ross in a statement Wednesday. “The Department of Commerce’s Bureau of Industry and Security will conduct a thorough, fair, and transparent review to determine whether uranium imports threaten to impair national security.”

The investigation will address all aspects of the uranium industry, including mining, enrichment, defense, and industrial consumption.

Two American uranium producers, Energy Fuels and Ur-Energy, petitioned the government to launch this investigation back in January, citing concerns over the amount of foreign state-subsidized uranium being imported.

“Despite uranium’s critical role in supporting clean electricity and national defense, imports of cheap, foreign state-subsidized uranium have swelled in recent years to the point that domestic suppliers currently provide less than 5% of our nation’s demand,” they said in a statement.

According to these companies, “the combined uranium imports from three geopolitically and commercially linked countries – Russia, Kazakhstan, and Uzbekistan – fulfilled nearly 40% of U.S. requirements” in 2016, and China has increased their own nuclear power production in recent years as well, threatening U.S. markets.

The World Nuclear Association states that just 7% of the uranium delivered to U.S. nuclear power plants last year was sourced from American companies. Canada was the largest individual foreign supplier, producing 35% of uranium purchases by U.S. plants.

According to CNBC, a 1962 law allows the president to tax imports if they’re considered a threat to national security. Tariffs on uranium could raise costs in the nuclear energy sector, which is already struggling from competition with natural gas and renewable energy. The Department of Commerce states that 20% of the U.S. electric grid is powered by nuclear energy.