The U.S. Trade Representative has concluded that Vietnam's actions and policies related to currency valuation are problematic for U.S. commerce. They determined that Vietnam's management of its currency, particularly through excessive foreign exchange market interventions, gives it an unfair advantage in international trade. These practices were found to be unreasonable, burden or restrict U.S. trade, and therefore can be addressed under Section 301 of the Trade Act of 1974. The U.S. is considering further actions to address these issues.
Simple Explanation
The U.S. is upset because they think Vietnam is not playing fair with money rules that make them do better in trading stuff with other countries. They want to find a way to make it more fair, but they arenβt sure yet what exactly theyβre going to do to fix it.