I actually had a contracting outfit once ask me to provide my last years return and pay stubs, they had some work at Saber they needed someone for. I was in a bad spot at that time and it was the only contract on the horizon so I politely told them that we agreed on a rate and that if they use that information to leverage a lower rate against me that I would double my rate. I think at the time I was trying to do $10 an hour more over the last year. Anyways, they swore up and down that it would not be used to leverage me down. They did, as soon as they had decided on picking me up, not only did they try to negotiate me down, but they also tried to push me 5hr below my last gig. I doubled the rate, would not budge and their client Saber was getting annoyed on the length of time it was taking to complete the contract. Meanwhile, a contract with Marriott came up that paid my rate no questions asked. I learned my lesson on that one, I never divulge salary information to a prospective contract. I simply state that my rate is my rate.
I went with a "total comp" number that included salary + signing and annual bonus as my previous salary. It ended up being a 20% raise when the new company matched it.
