Employers can verify your employment history in regards to job title and job description, your starting and ending dates of employment, and your salary.
Some employers verify work history directly, others outsource this task to third party reference.
There are no laws that limit what can be asked about prospective employees.
Organisations can call former employers and share the information which you have supplied in your resume or job application and ask previous employers to confirm its accuracy.
In some cases, employers or the firms they contract will conduct more extensive background checks which may also include an evaluation of your credit history and criminal record, depending on the type of job you are applying for.
If an employer conducts a background check, they are not limited to checking just the information you list on your resume or a job application. Don't think that because you didn't put it on the application form or resume that the employer won't find out about it.
It also depends on what the company is asking you to provide.
Be sure that you provide accurate information on your job applications and resume. Don't guess as to where you worked when. If you don't remember the details recreate your work history before you apply.
The bottom line is that it's important to be truthful with all information that you supply to prospective employers.
Courtesy: www.thebalance.com
