Stealing a Social Security number from a job application is one of the most common reasons for identity theft, so you have a right to be tepid about asking for a SSN on one, according to the Social Security Administration. You will have to get a SSN from employees eventually, but usually not right away.
You can ask for a SSN on a job application. You must eventually ask for a SSN, because the federal government keeps track of worker records with the Social Security database. You also need a SSN to verify the identity of a worker. If the Social Security Administration has to correct records, they will charge your company extra processing fees and the worker may lose on some SS earnings. (ref 2 and 3)
Civil service positions within the federal government require the job applicant to put his SSN on his resume, as of 2011. When possible, you want to limit requests for a SSN because the more sensitive data you have on people, the greater the risk of a rogue employee stealing that number to take out credit cards and commit other acts of identity theft. You could be found liable for data breaches, such as when you do not perform due diligence on an employee who steals company data.
Large businesses usually can wait until it needs to perform a criminal background check to get a SSN from a job applicant. Small businesses often forgo asking for a SSN for a criminal background check and instead call personal references. This also saves money on paying a third-party to research a potential hire.
Review your state's privacy laws, because some states prohibit employers from asking for an SSN unless they use a secured data line. Also, consider waiting to ask for a SSN until you are ready to hire someone or need to do further investigation on a few potential candidates, suggests Triad Careers.