Usher's ex-wife wants to take away his kids... claiming the singer has repeatedly blown off his legal obligations as a co-parent... and even worse he CLOSED her Saks 5th Avenue credit card... this according to court docs obtained by TMZ.  Tameka Raymond who had 2 kids with Usher during their brief 2 year marriage filed court papers in Georgia... asking a judge to strip Usher of joint physical custody of their children ASAP.

According to the docs, Tameka claims Usher has repeatedly FAILED to obtain her permission to travel outside the state with the kids... which he's legally obligated to do.

Me and my ex-wife were together for 12 years and had two kids. After years of her partying and not paying bills to support our family and bingo nights three times a week she decided that she had enough and it was time to call it quits. I came up with a plan that allowed us both to see OUR kids (KEY WORD)50/50. I moved into the same apartments as her, which was almost an hour from my job so we both could keep them 3 1/2 days per week and I paid all of the daycare expenses. I made an attempt to basically go beyond what was fair.