Green card holders pay U.S. tax on foreign income, even when they don't reside in the U.S.
For example, my Australian friend moved to NY to work at a law firm and received a Green Card. He then spent 4 years at that firm's Hong Kong office. He was required to pay U.S. income tax on the income he earned in Hong Kong, which was hard to swallow as Australia (like most countries) did not have the same requirement.
Many U.S. green card holders renounce their permanent resident status if they move back overseas for this reason.
For example, my Australian friend moved to NY to work at a law firm and received a Green Card. He then spent 4 years at that firm's Hong Kong office. He was required to pay U.S. income tax on the income he earned in Hong Kong, which was hard to swallow as Australia (like most countries) did not have the same requirement.
Many U.S. green card holders renounce their permanent resident status if they move back overseas for this reason.