You can also contact REBNY and check with them if they have a procedure to file a complaint.
What are the broker's explanations on why he does not want to pay commission?
One would need more information to give you a more soid advice.
1. Gather up and make copies of all paperwork related to your deals. You are required to keep all paperwork for 3 years anyway, so this should be easy. You might also want to ask former customers/clients if they would send you a copy of their commission checks to prove the money was paid. For all new deals, get copies of *everything* including checks prior to handing them to broker. Make sure your name and signature are on everything possible.
2. Keep all emails related to broker and all deals.
3. Locate whatever paperwork you did sign with the sponsoring broker. You should have signed something; find it. If not, no worries for right now. Find some evidence you worked there, though, even a website page can be printed and saved.
4. Immediately find another broker who will accept you as an agent. Ask your current broker to end your affiliation on line so you can affiliate with another firm. Broker has 5 business days to comply; if they refuse to release your license, you can *call* DOS. Timing for this may be tricky since you have pending deals, but this is where you are heading.
5. You can file suit in small claims court in NYC online. It's cheap and easy to do.
6. Note: do not let your license lapse. Only licensed individuals can legally collect commissions.
Finally, if broker is a member of REBNY and you are, too, you might want to call them.
You do not have to have an independent agreement in place, many offices do have one to avoid confusion about issues that could come up but it is not required. The agreement discloses the commission rate agreed, who pays for ads, if you are required to do floor duty and stuff like that. It is not the same as establishing association or affiliation with a real estate company. I am guessing you don't have one or you would know what it is.
Just happened to me around April of this year, taking this former broker of mine to arbitration, provide all the proof of chain of events of all your deals, I'm sure justice will be on your side. Also hire an attorney if possible.