When applying for immigrant visas(include K1 visa) and green card, proof of income and tax paying history is accomplished by requesting tax transcripts from the Internal Revenue Service.
These transcripts contain the amount of money paid and most form line items including your adjusted gross income (AGI) from the original tax return (Form 1040, 1040A or 1040EZ). It doesn’t show changes made after the filing the original returns. This transcript is only available for the current tax year and returns processed during the prior three years.
In order to request tax transcripts, a person must have a social security number or tax ID number, and know the address they filed from previously.
Tax Transcripts can be requested by mail or online from the IRS website.