Congress is showing some unease with the Trump administration’s use of an obscure trade law that addresses concerns over national security. House and Senate lawmakers signed letters to U.S. Commerce Secretary Wilbur Ross and Defense Secretary James Mattis warning that imposing tariffs on aluminum imports could increase costs for consumers and industrial users of the metal, according to documents obtained by Bloomberg. The letters said that can sheet used for food and beverage containers may be among products affected. The bipartisan warning comes two months after the Trump administration launched a so-called Section 232 investigation into aluminum. The government is probing whether foreign imports of the lightweight metal are damaging U.S. manufacturers severely enough to threaten national security. While the Obama administration had filed a World Trade Organization complaint that Chinese subsidies were stoking a global glut of the metal, Ross said the defense “angle” focuses on whether domestic manufacturers would be able to meet the Pentagon’s needs in the event of war. ‘Very Important’ “We hope that your investigation under Section 232 will be limited in scope to only products that are used for national security applications,” 44 lawmakers, including including Mike Coffman of Colorado and Ron Kind of Wisconsin, said in the House letter. “Not all aluminum is the same, and the distinction of rolled can sheet, and primary and ingot used for food and beverage containers, lids and closures versus other aluminum is very important.” Aluminum for three-month delivery has increased 10 percent this year on the London Metal Exchange, helped by China’s plans to curb excess production and steady global demand. The steel industry is awaiting a decision by the administration by the end of this month on a separate 232 investigation. The Senate letter, signed by eight lawmakers, said that tariffs could also affect manufacturing jobs in industries that rely on those products. At a public hearing in Washington last week Alcoa Corp., Rio Tinto Group and Arconic Inc. stopped short of backing Trump’s import crackdown. Arconic, one of the biggest American producers of aluminum automotive and jet parts, warned that action on imports of raw metal may disrupt the supply chain.