Question about the government! And paying taxes!!!7?

Ok going to try and make it quick..... say someone is getting cash without having a job... and they are depositing it into a bank account. Only about $200-$500 at a time. Can the government actually go into someones account and look.? And if they suspect that taxes were not paid can they go after someone and charge them with something... If you have links and evidence thats a bonus! *** Honest answers people and dont be rude either.