A week ago, Kevin Federline grudgingly consented to allow Britney Spears overnight visits with sons Sean Preston and Jayden James.

It didn't take long for him to change his mind.

During a closed-door emergency hearing Wednesday, Los Angeles Superior Court Commissioner Scott Gordon suspended Spears' visitation rights until she complied with his full custody order, which includes parenting sessions and random drug tests.

The decision has devastated the singer.

"She's really upset," a source close to Spears tells E! Online. "She keeps saying, 'I can't believe this is happening.' It's like she just can't accept what's happened."

A second source familiar with the ongoing custody tug-of-war tells E! Online Federline was so angry when the children came back to him after their last visit with Spears two days ago he vowed to do whatever it takes to keep his ex-wife from seeing their babies again until she cleans up her act.

"She just doesn't take parenting seriously," the Federline insider says. "And Kevin knows it. He keeps saying he's genuinely scared for their safety." And not even a court-ordered monitor has changed that.

"He knows that even with monitored visits, no one can make Britney do what she doesn't want to do," the source adds. "She's used to telling people what to do, pushing people out of her way. She's a hard woman to control."

Federline was convinced Spears wasn't living up to her maternal responsibilities after the kids came back to his house crying and surly.

"They came back to his house, and their eating schedule was off, their sleeping schedule was off, and they won't listen to him, because he knows they haven't been getting any discipline at her house," the Federline associate claims.

"He has to start all over, getting them settled again, calm them down and reintroduce them to their normal schedules. And it's frustrating for him. He's been tolerating this for a long time, but he thought maybe it would get better with a monitor involved. It hasn't."

During the last dropoff with the kids two days ago, eyewitnesses say Spears appeared to be in a very foul mood, even snapping at her brand-new assistant.

"She was walking very fast and then bitching because her new assistant wasn't walking fast enough to keep up," recounts the insider from the Federline camp. "She kept saying things like, 'Oh, come on! Will you hurry up?' And it just made the whole situation so tense for everyone."

Federline heard about how ill-tempered Spears seemed after the fact, because he doesn't go to the dropoffs himself, instead preferring to let security bring him the children.

"He just knows he can't see her, because she is so unapproachable, and he's afraid she'll get all bananas in front of the kids, like she used to when they were married," the K-Fed source says.

Federline is also concerned about the level of paparazzi attention to Spears' every move.

"When they were married, they had a dozen or so photographers following them around," the Federline insider continues. "But now, she's got this unmanageable horde around her all the time. Sometimes 50 or more people are all around her, and what kind of affect does that have on the kids? But Brit doesn't care anymore, she just acts like it's all so normal."

Federline turned to his lawyer, Mark Vincent Kaplan, for help once again, asking him to look into how the monitored visits are going and whether Spears had been going to the parenting coach. She apparently had not. She also may not be in full compliance with the court's drug-test order.

"So, Kevin wanted back in court right away to see about cutting off her visits," the Federline source explains.

"Kevin believes it's the only way she'll start paying attention to her responsibilities, by making her feel the consequences of shirking them."

A rep for Kaplan tells E! News that Spears is working to follow the judge's order and should regain visitation in the coming days. The parenting coach is due to submit a report at the next hearing on Oct. 26, when Gordon may modify the custody arrangement yet again. Spears and Federline are both expected to attend.