help: A copy of reference letters from any previous U.S. employer(s)?

[blue-snow]

Hi Dear friends,
I am starting to apply the Alberta Immigrant Nominee Program (H1B Holders) and do need your help.

I have been borthered by one required document in the H1b_AINP009 form, "A copy of reference letters from any previous U.S. employer(s)"
Does this mean a recommendation letter or just a employment certification letter? If that is just an employment certificaiton letter, can I use the offer letter for replacement (I have related W2 form)? I have two previous US employers, Can I only send the letters from one of the US employers?

I really do not want to contact my previous employer to request a recommendation letter. She is unhappy with me because I left her lab. If she is a good boss I will not leave her lab. She is just a monster.

I appreciate any of your informaiton.