Can I put a block or a pin number on my son's social security number to prevent his dad from claiming him on his taxes? He doesn't support him anymore.

My son's father has been claiming my son for the past nine years now. But for the past year and a half almost two years now he has stopped providing for our son. My son is now ten years old. He was allowed to claim him as long as he provided for his son financially and consistently. However, this has stopped unfortunately. He told me that he will continue to claim him whether he is providing for him or not because he has been claiming him on his taxes for years now. Also since i am the only parent that is now supporting him by myself I wanted to claim my son for the very first time this year.