The phrase "big loophole" refers to a significant gap or weakness in a rule, law, or system that allows someone to avoid or exploit its intended purpose.
Sentences with «big loophole»
Loopholes in campaign finance laws: There are two big loopholes in campaign finance law. (syracuse.com)
In Hillsborough County, there's an even bigger loophole around the law. (wfla.com)
That's because, as is all too typical with US gun laws, the automatic weapons ban has some pretty big loopholes. (vox.com)