If you are an undocumented immigrant, it can be a crime to work in the U.S. and not pay taxes on your income. You must pay taxes on income earned from employment in the U.S., even if you are not lawfully in the U.S.
If you work in the U.S. you are required to file taxes. By filing taxes, you may be eligible for refunds of the taxes that are withheld from your paycheck.
Filing taxes can help with an immigration case. For example, filing taxes is evidence that you are a person with good moral character. It shows that you respect and follow U.S. laws. Showing good moral character is important when applying to become a U.S. citizen and for other types of immigration cases. Filing taxes can also be used to prove the number of years you have lived in the U.S., which is very important for immigration.