Safe deposit boxes may be frozen or accessed if there is a judgment against your assets. These judgments can come either from private party judgments, such as collections agencies, or the IRS. Since you must supply your name in order to open a safe deposit box, the IRS can trace that box if they have reasonable cause. You cannot place assets in a safe deposit box without identification to prevent against crime and money laundering.
When you owe money to the IRS, they have a lot of power over your assets. They can place a total freeze on your money, including savings accounts, safe deposit boxes and even income. The freeze may not be lifted until you pay. IRS judgments are senior debt, meaning they will take priority over other forms of loans.
You are protected against unwarranted search and seizure in the United States. This means the IRS is not permitted to simply freeze or check your assets at will. However, if the IRS has reasonable suspicion you owe money, they can submit a written request to the banks or vaults where you hold your monies. These requests are similar to warrants; they must provide some details of the crime you are being accused of.