The Houthis have shot down multiple American MQ-9 Reaper drones as well.

The last Houthi maritime attack came on Oct. 28 and targeted the Liberian-flagged bulk tanker Motaro. Before that, an Oct. 10 attack targeted the Liberian-flagged chemical tanker Olympic Spirit.

It’s unclear why the Houthis’ attacks have dropped, though they have launched multiple missiles toward Israel as well. On Oct. 17, the U.S. military unleashed B-2 stealth bombers to target underground bunkers used by the rebels. U.S. airstrikes also have been targeting Houthi positions in recent days as well.

Meanwhile, a report by U.N. experts from October says “the Houthis allegedly collected illegal fees from a few shipping agencies to allow their ships to sail through the Red Sea and the Gulf of Aden without being attacked.” It put the money generated a month at around $180 million, though it stressed it hadn’t been able to corroborate the information provided by sources to the panel.

The Houthis haven’t directly responded to the allegation. However, the report did include two threatening emails the Houthis sent to shippers, with one of those vessels later coming under attack by the rebels.