You can ask questions about citizenship in pre-screening. There would potentially be three reasons you'd ask this question. First, you may be required by your contracts to employ only U.S. citizens. Second, you may not have the financial resources to offer sponsorship. Third, you may be looking to ensure that you don't employ persons who are ineligible to work in the United States. In order to avoid any issues regarding discrimination based on national origin, you may want to ask questions along the lines of the following: 1. Are you legally eligible to work in the United States? 2. Do you require sponsorship in order accept a position with our company? There would be a variety of other ways to get this information, but the questions above don't ask about nationality or race in any way.
You can use this OFCCP audit checklist to ensure you're doing what is required to maintain OFCCP's regulations including VEVRAA, Section 503, and EO 11246. Or request a demo to streamline your compliance and recruiting efforts.