President Donald Trump said Thursday that Iran must not impose charges on vessels passing through the Strait of Hormuz, as shipping activity remains sharply reduced following the outbreak of war and the waterway’s effective closure.

In a post on Truth Social, Trump addressed reports that Tehran may be seeking to collect fees from tankers navigating the critical passage. “There are reports that Iran is charging fees to tankers going through the Hormuz Strait,” Trump wrote.

He followed with a direct warning, stating, “They better not be and, if they are, they better stop now.”

Speculation has grown in recent days that Iran is considering introducing tolls for ships using the strait, a move that has been firmly rejected by Western officials who oppose paying for passage.

According to a report published Wednesday by the Financial Times, an Iranian official indicated that Tehran intends to require payment in cryptocurrency from ships in order to maintain its grip on the strait during a temporary two-week ceasefire with the United States.

In another message posted Thursday, Trump hinted at developments in global energy flow but did not provide details, writing, “you’ll see Oil start flowing, with or without the help of Iran.”

Earlier this week, Trump declared a ceasefire with Iran, following prior threats in which he warned of catastrophic consequences for the country.

Despite the ceasefire, maritime movement through the Strait of Hormuz remained at less than 10% of typical levels on Thursday. Reuters reported that Iran has continued to assert control over the area, instructing ships to remain within its territorial waters as they transit the route.