If the sponsoring spouse (or joint sponsor, if any) did not file taxes in the previous year, they will need to include an exemption letter explaining why no taxes were filed.
The spouse seeking a green card, either from within or outside the United States, does not need to include an exemption letter if no U.S. federal taxes were filed, and they also do not need to include any foreign tax returns.
Learn more here about what to do if either spouse did not file any taxes.
What is continuous physical presence?
To be eligible for citizenship, an applicant must have continuously lived in the United States as a green card holder for at least five years (or at least three years if they’re married to a U.S. citizen).
“Continuously” means they did not take any trips outside of the United States that each lasted six months or longer during the 3–5 years they were required to have a green card (plus the extra period while U.S. Citizenship and Immigration Services (USCIS) processes their U.S. citizenship application).
In other words, an applicant is allowed to leave the United States — they just have to make sure to return within six months every time.