All persons working in the US have their salaries deducted to cover the advances on income tax. The advances depend on the State they work in and amounts between 10-20% of  the income.

When back in Poland it's advisable to claim your tax refund. To get it done it's required to submit the tax return to the IRS (Internal Revenue Service) listing incomes from all the employers.

The taxes you pay during work time are as follows:

• Federal tax – constitutes 10% of income and rises along with the income.
• State tax – its refund depends on the tax law in a particular state. It constitutes 1-10% of income. That kind of tax is not collected in following states: Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington and Wyoming.
• Local tax – constitutes approximately  1-2 % of income and is not refundable.
• social security tax and medical tax