Can non-custodial parent claim child when other parent doesn't work or file?

[quesadaddy]

I am in California.  My ex and I have shared 50% joint legal and physical, but for tax purposes she would be considered the custodial parent.  She has not worked for 8 years and does not file taxes because of this.  

Can I claim our child?  I have over the past few years without issue but this year she had her boyfriend claim him (and my efile was bounced back) and is stating that I was illegally claiming him.  I believe as the biological father, I have the right (next in line kind of thing).  She is claiming I need a special form signed by her which I would agree with 100% if she filed taxes.

Thanks in advance.  

[JotikaT2]

It depends.

In order for you to continue to claim the child on your tax return as a dependent, you will need to obtain a signed Form 8332 from the custodial parent allowing you to do so.

Otherwise, if both claim the same child, the IRS will usually give the dependent claim to the parent the child lived with the most during the year.

Information for Form 8332 - Release/Revocation of claim to exemption info

Form 8332

Dependent requirements

Dependent dilemmas