The Fair Credit Reporting Act, a federal law, requires that you are required to know when a background check is being performed on you, although there is one possible exception. These checks are normally performed by businesses as part of pre-employment screening, and the FCRA applies to background or consumer checks performed by a third party in exchange for financial compensation.
In order to conduct the background check, an employer must first have written permission from the person the check will be performed on. This notice of a background check must be on a separate sheet of paper than the rest of a job application. However, federal law does not require that the results of the screening have to be made available to you, although some states do require this. If a background check leads to adverse consequences for you, such as being denied employment, denied promotion, or being fired, the employer does have to provide a copy of the background check. They also must provide contact information for the screening company, so that you can dispute the results if there is incorrect information contained in the report.
If the company you're applying to or work for does a background check on their own, without contracting a third party entity, they are not required to provide forewarning to you regarding the screening. Additionally, the company would not have to provide a copy of the background report. If you are fired or denied employment and the company claims this is for other reasons, they would not have to provide a copy under the FCRA, either.
Some state laws close these loopholes in the FCRA by mandating that subjects of background checks are able to receive a copy of the report whether or not adverse actions were taken. These state laws also ensure that employees have to be notified of background checks even when a company performs them on its own.
Make sure that you know your rights with regard to background checks, both under the FCRA as well as with regards to state law so as to avoid being surprised by any background checks you could undergo. It is your right to know what is on your background check and your responsibility to yourself to find out.