American citizens do not need passport to go to Canada, Mexico, Bahamas and maybe few other neighboring countries. This law will put a stop to that. Nexus is a document provided to Canadians and Americans who submit to pre-screening and need to cross the border frequently. With Nexus, you can proceed to fast lane and, as your background is already checked, they won't scrutinize your documents as much and saves you time at the border. If you are a PR, it just means you will have to carry your green card and your country's passport with you whenever you travel. That's all.