"You cannot end birthright citizenship with an executive order," Ryan told WVLK Radio as quoted by The Washington Post.
Earlier on Tuesday, Trump told Axios in an interview scheduled to air Sunday on HBO, that he would sign an executive order to end to the "ridiculous" practice of granting birthright citizenship in the United States.
READ MORE: 'It'll Happen': Trump Vows to Terminate US Birthright Citizenship
Birthright citizenship is anchored in the 14th Amendment to the US Constitution adopted in 1868.
In order to change a constitutional amendment, it must be passed by two-thirds of the US House and Senate and then ratified by 38 of the 50 states, which amounts to three-fourths of the US states.