contractor refuses to pay full amount to me subcontractor

I am a subcontractor who does foreclosures. I recently did a job in maryland removing 380 cubes. to this date have only been paid for 30 cubes. Now that they are about to cut a check the owner of company I contract went in and removed another 2000.00 from my contracted price. I am told that must accept this or get nothing. I am lost as to what my next step should be