Crypto scammers are targeting the thousands of ships stranded near the Strait of Hormuz, and at least one vessel that faced Iranian gunfire may have been deceived into believing it had paid Iran for safe passage.

The first warning of this crypto scam came from MARISKS, a Greek maritime risk management company, on April 20, according to Reuters.

The company alerted shipowners that fraudsters posing as Iranian authorities had sent messages demanding “transit fee” payments in bitcoin or tether.

This scam is particularly confusing for shipping companies because Iran has tightened control over the Strait of Hormuz—a critical shipping route and maritime chokepoint that typically accounts for one-fifth of the world’s oil and liquefied natural gas supply.

Iranian authorities have previously demanded cryptocurrency payments from oil tankers to pass through the waterway and required ships to follow a route near Iran’s coastline for inspection.