Can your employer withold your earnings because of a

I work online. The website company takes about 45-60% commission out of every online chat/email session that I do for a client.

However, one client from that website contacted me, and I gave them my personal email and my own personal website (due to paypal takes out less comission) and I needed the money. The website then decided to "fine" me and withold over $1000 of my earnings (this is after commission was taken out)...being that I am an "independant contractor" on their expert website, is this legal on what they did? I know they take out commission, etc..but witholding my paid earnings because I "steered" a client away from their site---is this legal?
Their website is located in NY state, so how does that apply to laws for anyone who gets a "fine" on their website they work for?
Thank you for your advice.