Hi and welcome to Just Answer!Are you US citizen?
Assuming you are NOT an US citizen - and are a nonresident alien - the general rule is - pension income related to past employment in the US is considered income from US sources and as such is taxable in the US.However - because you are a resident of Turkey - you should be aware of the tax treaty between the US and Turkey which overrides the general tax law - see page 20 - http://www.irs.gov/pub/irs-trty/turkey.pdf - ARTICLE 18 Pensions and Annuities
1. Subject to the provisions of paragraph 2 of Article 19 (Government Service), pensions and other similar remuneration paid to a resident of a Contracting State in consideration of past employment, whether paid periodically or in a lump-sum, shall be taxable only in that State.
So far - US pension should be only taxed in Turkey and should not be taxed in the US.
What you need to do - provide a signed form W8BEB to the payer and mention that paragraph of the tax treaty as an exclusion from ANY withholding.Here is the form to print - www.irs.gov/pub/irs-pdf/fw8ben.pdf
To claim a refund for taxes that were already withheld - you need to file a tax return as a nonresident - form 1040NR - www.irs.gov/pub/irs-pdf/f1040nr.pdf and claim pension income as not taxable based on the tax treaty I referenced above.Let me know if you need any help or clarification.
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Appreciate your warm words. Just want to let you know that I am NOT an attorney and not a CPA - but I do tax preparation. My goal is to provide EXCELLENT service - and I will address all your concerns and tax related issues. Please feel free to ask for clarification as needed.
You may also review my other answers - http://www.justanswer.com/finance/expert-lev-tax/questions.html