Can a HR rep contact another company to verify the salary of a applicant applying for a job?

If an person is applying to another company, can HR of that company contact the person current employer to verify the person's current salary it stated on the application?

I know in NY they can only verify that you did actually work for the company during the time you stated. No other information can be provided, however, if you provide the new company with your SS# to do a background check they will be able to see all the jobs you've held and the salary/wages you received. IMO, just don't lie, it will come back to haunt you.

most places require a form signed by the applicant
Yes, they can. They have the right to check the truth. Their job is to find the right person for the right place. Sometimes they just did it because they want to be sure of that person, before they make an offering. Tell the truth even though you asked your salary for the new company twice than the previous company.
I believe that information is considered private and can not be released unless the prospective employer has a signed authorization from the employee.
what I understand is they can only ask if you worked there and how long.
I think it depends on the state you're in. Like in MI, you're by law only allowed to verify dates of employment. Any other question beyond that is illegal.