Tameka Foster, who split from the singer in 2009, lost custody of their sons Usher Raymond V, five, and Naviyd, four, last year but filed legal documents on Tuesday asking for an emergency hearing later this week, just one day after Usher Jr. allegedly almost drowned in a swimming pool when his hand got stuck in a drain.
A source told gossip website TMZ.com that Tameka, a former stylist, plans to argue that the boys are in a dangerous environment and The Voice mentor should not be their main carer.
She filed documents in Fulton County in Georgia, claiming her 34-year-old ex-husband is abdicating his parental responsibilities by letting other people care for their two sons - who she claims are not supervising them enough.
Tameka, who currently only has limited custodial rights of the boys, wants to reverse the situation.
Usher Jr. remains in an Intensive Care Unit (ICU) in hospital in Atlanta, Georgia, following his accident while swimming.
The little boy was playing in the water with his father's aunt when he dove down to retrieve a toy that was lying in the drain. His arm got stuck and the aunt and a maid were unable to free him.
Two men, who were working at the property, jumped into the pool and were able to get him out and lay him beside the pool, where he was immediately given CPR before being rushed to hospital by an ambulance.
Doctors are still running tests but believe he will be okay.
Tameka's 11-year-old son Kile, from a previous relationship, died last year after a Jet Ski accident.
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