Agency guidance documents do not have the legal force of law, but they are practically binding because they state the agency's current policy on a particular issue. USCIS heavily relies on its own guidance documents to conduct its adjudications. Agency documents are sometimes referred to as "sub-regulatory" or "nonlegislative" rules because they are not the product of public notice and comment rulemaking. Deciding whether an agency has properly used the policy statement exemptions from notice-and-comment rulemaking is hard. A court will only attempt to decide if an agency properly invoked an exemption after the fact.
Refer to the immigration regulations tab of this guide for a discussion of immigration rules that have to follow the notice and comment procedure of rulemaking.
Refer to the sub-pages of this guide for USCIS guidance, Executive Office of Immigration Review (EOIR) guidance, and State Department guidance.