Iran doesn't have legal control over the entire strait; approx half of the strait is Iranian territorial waters and the other half is Omani territorial waters.

For Iran's toll system to work, they would need to strike at ships sailing in Omani territorial waters, which is an act of war.

international law doesnt actually exist. the strait is close enough to irans borders such that they can enforce police activity, so its theirs.

the alternative is that oman and many others can also do the same thing, and the lot of states interested in trade in the area need to get together an negotiate a setup that everyone can agree to

but iran has physical control. lets call it a buffer zone for toll collection. And funny that you mention act of war like it was(would be) caused by iran.