Vessels seeking to transit the Strait of Hormuz under Iranian protection are being asked to provide lists of crew and cargo, along with voyage details and bills of lading, in order to secure a green light from the Islamic Revolutionary Guard Corps.

The process is still idiosyncratic and can vary from ship to ship, according to accounts from people familiar with the trade, but it points to Iran’s increasing efforts to assert control over the vital maritime channel with a semi-formal system as the conflict in the Persian Gulf extends into its fourth week.

Iran has requested payments from some but not all ships, according to the people, asking not to be named given the sensitivity of the discussions. These demands — channeled through intermediaries, and of differing size — are generally reserved for oil tankers, gas carriers or other vessels with high-value cargoes, they said.

Since U.S. and Israeli strikes began almost a month ago, only a trickle of vessels have made it through the waterway, many of them Iranian or China-linked tankers. Those making it through with apparent protection from Tehran have mostly followed a similar route, hewing close to Iran’s coastline.

Iran said in a communique earlier this week that navigation continued for vessels from friendly nations “in co-ordination with the competent Iranian authorities.” While Iran’s Supreme Leader Mojtaba Khamenei has said Iran should keep the strait shut, the letter said the waterway remained open and “traffic has not been suspended.”

The IRGC said on March 24 that it had turned back a container ship for failing to comply with legal protocols and lacking permission to transit the strait.

After U.S. President Donald Trump set a 48-hour deadline over the weekend for the reopening of Hormuz and then pushed that back, the U.S. government has been pressing for talks with Iran. Developments including a 15-point plan to end the war have helped cool soaring oil prices on March 25 — but there has been little sign of letup on the ground, or of immediate changes to traffic around Hormuz. 

Asian countries have been acutely affected by the disruption in the energy trade from the Persian Gulf, with shortages of fuels across the region. India, among the most impacted, has seen a severe shortage of liquefied petroleum gas. Only a handful of Indian LPG tankers have made it through the strait — after talks between New Delhi and Tehran.

India has said international laws guarantee the right of freedom of navigation through the strait, meaning no fees could be charged. 

Chinese government agencies charged with supervising shipping are aware of protection fees paid by some Chinese vessels through local agents, one of the people said, adding officials see little basis for such charges. That’s partly because transit rights are guaranteed by international law, but also because Beijing is a vital trading partner for the region and an economic lifeline for Tehran, buying up most of its oil exports.

Iran has said the full restoration of security and stability in the Strait is contingent on the end of military threats in the region.