Was wondering how this is going to affect US citizens living in Thailand?

If you are working does it mean you will have to pay tax to both Thailand and the US?

Will you have to put in tax returns whether working or not?

If you are a US citizen or green card holder you absolutely have to file US tax returns, wherever you live, regardless of your employment/ income status. The US and Thailand have a treaty which stipulates for income earned in TH, that you only have to pay the US the difference in tax between the Thai and the US rate. If you live/ work abroad full time, you may also be entitled to a foreign-earned income exemption up to a certain amount (I believe around $ 90K). You're also obligated to report all foreign assets, such as bank accounts, investments etc., each tax year.

My advice is, get some professional advice, as the new regulations regarding reporting are even stricter than before and come with truly draconian penalties. I'm talking to my accountant now to get ready for the next wave. By the sounds of it, being an US taxpayer living abroad is becoming a financial nightmare!

Quite a few ThaiVisa threads on FATCA. Just enter FATCA in the Search field.