A job offer is required and the U.S. employer must file an Immigrant Petition for Alien Worker, Form I-140, on behalf of the applicant. You must provide proof of current income with the I864.A letter of future employment is not proof of current income. The job offer letter should be on company letterhead and state the position you are being offered, your start date, salary and benefits. Learn the uses of an employment verification letter (EVL), what it should contain, and how to request one. Plus, download free customizable templates. An employment verification letter can help prove income for a green card. Find a sample employment verification letter for immigration here. Employment Offer Letter. Our experienced attorneys provide innovative solutions for US employers and international business professionals.