A model L-1B specialized knowledge worker petition or L Blanket application support letter. This letter is used by employers to support L-1B nonimmigrant visa petitions to US Citizenship and Immigration Services (USCIS), L Blanket applications to a US consular official, or a USCIS petition or L Blanket application by a Canadian citizen to an immigration inspector at a port of entry. This Standard Document has integrated notes with important explanations and drafting tips.