Federline was furious the "Toxic" star had checked out of Promises in Malibu last Wednesday and worked with his lawyer, Mark Vincent Kaplan, to schedule an emergency hearing to seek physical and legal custody of their sons, Sean Preston, 18 months, and Jayden James, six months.
A source tells People magazine Federline gave his estranged wife a choice--either she checked back into rehab that night or he would go to court the next morning.
Spears showed up at his home in Tarzana, California, last Wednesday evening, followed by 20 members of the paparazzi. When Federline failed to appear, she left and was later seen hitting a photographer's car with an umbrella.
Later that night, Spears' mother Lynne, who had flown in from Louisiana to look after her daughter and grandsons, drove her back to the rehab facility.
A source says, "Kevin is working closely with Lynne to let Britney know how serious it is that she gets help."
Federline reportedly played a key role in persuading Spears to seek treatment in the first place and has regularly been spotted visiting her at Promises.
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