A group of families whose loved ones died of fentanyl overdoses filed a petition with the office of U.S. Trade Representative Katherine Tai on Thursday, requesting a probe into China’s alleged role in fueling the U.S. synthetic opioid crisis.

The petition was filed under Section 301 of the Trade Act of 1974, a statute that allows the U.S. to impose sanctions on foreign countries that violate trade agreements or hurt U.S. commerce. The families are seeking trade countermeasures that include tariffs of at least $50 billion on Chinese merchandise.