Alien Employment License Number is it the one with 11 digit number?

Hi,
I am applying for my work Z and on the Supplementary Form it asks for an Alien Employment License Number. I'm not sure if I have this number or not. I have received a working permit. It has an 11 digit number on it followed by the letters WP. Could this be my Alien Employment License Number?
I appreciate any help, Thank you.
Jin Chen