In general, the IRS requires the spouse's SSN so they can compare the two spouse's tax returns, because when spouses choose to file MFS, there are some credits and deductions that are reduced or not allowed and some other special rules apply. In your case, you need to indicate "NRA" in the space for the SSN, and that requires printing and mailing the return. Turbotax does not support e-filing for an NRA spouse.
