All Foreign mariners working in the US Outer Continental Shelf / Gulf of Mexico are now required to pay US taxes and FICA as of January 01, 2009.
Most likely thier company will pay the bill! When I was working in India on a Frac boat I was required to pay the Indian Goverment Taxes. I even got an Indiain ID card proving I was a tax payer. That cost was paid for by my company. Nothing out of pocket for me.
“Most likely” a 20 to 30 percent pay increase to offset the taxes.