Iran is in discussions with America's Gulf ally Oman over a possible partnership to make vessels passing through the Strait of Hormuz pay a fee, but it's not clear that it would be legal or that it would receive much support from countries using the waterway. 

Secretary of State Marco Rubio warned Friday that "no country" should accept any tolling system. 

“I don't know of anyone in the world that should be in favor of a tolling system in an international waterway. That's just not acceptable. It can't happen,” Rubio told reporters, according to Fox News.

Iran's Persian Gulf Authority, a newly created regulatory agency to oversee traffic in the Strait of Hormuz, said Wednesday that it had defined the boundaries of its authority within the strait, and ships passing through the territory would need a permit. 

Iranian ambassador to France, Mohammad Amin-Nejad, told Bloomberg that Iran and Oman were setting up a permanent toll system to formalize control of maritime traffic through the strait.

“This will entail costs, and it goes without saying that those who wish to benefit from this traffic must also pay their share,” he said. 

The New York Times, citing unnamed sources, said it isn't a toll system but rather a charge for services to pass through the strait, a major international channel for oil shipping.  

However it is described, such a fee system would be illegal under the 1982 United Nations Convention on the Law of the Sea, which states that vessels can traverse international waters so long as they comply with safety and pollution regulations, according to legal experts. While Iran isn't a party to the convention, Oman is a signatory. 

James Kraska, a professor of international maritime law at the U.S. Naval War College and visiting professor at Harvard Law School, told the Times that the rules reflect customary international law and are binding on all nations.