Lying to a federal investigator is an offense. It's usually how the feds get you if they can't make anything else stick (see Martha Stewart). Usually with the

Lying to a federal investigator is an offense. It's usually how the feds get you if they can't make anything else stick (see Martha Stewart). Usually with the border patrol stops a vehicle they ask if there are any non-citizens in the vehicle. If you lie at this point and they don't believe you it would likely give cause to investigate further. So either tell the truth or shut up. Given that any documented not-citizens are supposed to carry their permanent resident card or passport with them at all times then the assumption is that any not-citizens are doing just that so can easily prove their status. Not everyone does and in recent years they've been policing this a lot harder than they used to and you can find yourself in hot water if you encounter the wrong officer (most cases you will get a very stern talking to). So if you aren't carrying a permanent resident card or passport then the assumption is that you are either a citizen or undocumented. How hard they push to find out which depends on the bias of the officer making the stop.