Partial updgrading would free up pipeline space and produce a grade of oil that's easier to refine and more valuable than the heavy grades produced currently.
The cap, which was set at $70 per tonne for two years for coal with a calorific value of 6,322 kilocalories, will now apply from March 12, revised from Jan. 1, 2018 previously.
The National Mining Association (NMA) and the American Exploration and Mining Association (AEMA) have filed petitions asking the court to reverse the 2012 ban.
German Chancellor Angela Merkel said Europe must be ready to respond to the unilateral imposition of trade tariffs by the United States but she first hoped for talks on the issue.