L1 VISA Proof

Does anyone know what forms of proof of prior employment is required to obtain the L1 VISA? It is my understanding that the employee must have worked for the company (applicant) in the home country for at least 1 year and I am wondering what type of proof is expected to fulfill that requirement.
Thanks

A statement letter from human resources and a copy of pay stubs for a year or a copy of taxes paid should cover it.

Thanks for the reply, no sites I've seen so far have said what kind of proof is necessary.
One other clarification...the work was done as a consultant, i.e. husband consulted for parent company in Canada and invoiced accordingly, so would invoice dated for the prior period be sufficient along with letter from HR?

Be careful. Being a contractor will not qualify your spouse for l1.

For L1, the relationship must be as an employee, both before and after the transfer.

See: http://www.immigrateusa.us/content/view/19/33/

"The USCIS has recently clarified that the overseas entity must directly employ the beneficiary as an employee. Therefore, an independent contractor who performed services for a foreign affiliate will not qualify, even if these services were controlled and regulated by the foreign company."