US Supreme Court has decided to hear lawsuit questioning citizenship by birth.

The nation's highest court has agreed to take on a significant case that puts to the test a century-old guarantee: automatic citizenship for individuals born on American soil.

On the inaugural day in office this January, President Donald Trump signed an order aiming to end this practice, but the move was struck down by federal courts after constitutional questions were filed.

The Supreme Court's ultimate judgment will either affirm citizenship rights for the infants of migrants who are in the US without authorization or on non-immigrant visas, or it will overturn them altogether.

Next, the justices will schedule a date to hear the case between the federal government and the suing parties, which comprise foreign-born parents and their young children.

The 14th Amendment

For over a century and a half, the Fourteenth Amendment has codified the principle that all individuals born in the United States is a American citizen, with exceptions for children born to diplomats and personnel of invading forces.

"Anyone born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States."

The disputed presidential order sought to refuse citizenship to the offspring of people who are either in the US without legal status or are in the country on short-term status.

The United States is one of about a minority of states – mostly in the Western Hemisphere – that award instant citizenship to any person born in their territory.