Virtually all countries apply withholding taxes when local companies seek to distribute dividends to externally based shareholders (whether those shareholders are corporate or not).  The rate at which IBKR is obligated to withhold for a given payment depends largely upon whether there is a tax treaty in place between the US and the country of residence of the dividend recipient.  .

The table below depicts certain the rates of withholding as applied by IBKR effective 6-1-2012.