Employers are not legally "required" to provide any information about its employees to anyone. However, it has become modern day practice for most employers to confirm basic information about employees, such as confirming the dates of employment and the position held. More private information, such as the employee's wage should not be conveyed without the written permission of the employee.
Job references which indicate the employee's performance are legal, as long as they are truthful and honest. Many employers won't give them anymore, our of fear of being sued, but this is a matter that should be decided between the employer and the employee.
As an employer you don't have any legal obligation to provide employment verification information. I advise my clients to simply state: We have a policy to only provide the dates of employment and job title.