Does H1B require experience letter from past employee

Does applying for H1B requires me to provide experience/reference letter from my past employees ?

I also heard the H1B is much harder this year. Is that true ?

H1-B is based on having a 4-year bachelor's degree. If you do not have a degree, you would then need letters of experience, to cover 3 years per year of school missing. (ie. if you have no post-sec education, you would need 12 years (4 x 3) of documented experience).

Otherwise, nothing from past work is needed for h1-B petition.

I see. I do have a Bachelor of Math from Canadian University.

But, I was consistently rejected for TN VISA for Computer System Analyst category because my degree is not in Computer Science. I hope H1B won't be so strict.

Typically it is not. Thta is one of the only reasons for a Cdn professional to go H1 instead of TN.