Sometimes you wonder why employees have to ask about salary history. It is discriminatory especially to women and this is what has made women's salary to be at the same level, no increase at all. Employees will offer women the same salary as was offered in their previous place of work despite their male counterparts getting a pay rise from what they earned previously.
Another example of unnecessary probing into our personal lives. Businesses have no need for this information. Salary should be discussed in regards to what the company is willing to pay regarding the hire's qualifications. What this person has made in the past is irrelevant. However, if the hire chooses to bring up such information for negotiation purposes, then that is fine.
I think this is pretty standard. Any more info could result in a lawsuit. People who get fired often hire PI's to contact their former employer and pretend to be an HR rep asking about your reasons for being fired. Is there any possible benefit to the company to answer anything other than a "yes"?
There's nothing with asking about a salary history, because it helps offer a person what they're worth. It's not just women that face lower pay, men who take time off for family leave might have the same problems with salary history. Discrimination is a complicated issue but you should still be allowed to ask questions.