Foreign Investment in Real Property TAX Act of 1980

The disposition of US real property interest by a foreign person is subject to the FIRPTA Tax Act. 

Disposition means "disposition" for any purpose of the IRS code. This includes, sale, exchange, liquidation, gift, etc. Officers are required to withhold 15%. This is not your taxed amount. This is held until taxes are filed and tax amounts are determined. 

From irs.gov:

INSTRUCTIONS FOR FORM 8288 

U.S. WITHHOLDING TAX RETURN FOR DISPOSITIONS BY FOREIGN PERSONS OF U.S. REAL PROPERTY INTERESTS

 

Here is the IRS Link: https://www.irs.gov/individuals/international-taxpayers/firpta-withholding