As if their relationship wasn't toxic enough, Kevin Federline just added more drama to his custody battle with baby mama Britney Spears. The 40-year-old DJ filed documents on May 22 to increase the amount of money Britney pays him in child support each month. Now, Brit is reportedly worried that if she doesn't oblige, Kevin is going to keep their two sons — Sean Preston, 12, and Jayden James, 11 — away from her.

"Britney is extremely agitated and extremely concerned that Kevin is going to no longer allow her to see their children because he has sole custody as retribution for not agreeing to the $40,000 in child support payment," a source told Us Weekly. "[It] would be a $20,000 increase from what he is getting now."

kevin federline britney spears

The source added, "Britney's father, Jamie Spears, had signed off on a modest increase of $25,000, but demanded a monthly accounting of how that money was being spent." Because Kevin has four other children from different relationships, Britney and her father want to make sure she's not providing for anyone but the two kids she and Kevin share.

Although Britney is reportedly nervous that Kevin might pull a drastic move and keep her from seeing the boys, she feels like she has a right to know what he needs more money for. The songstress supposedly already pays for most of Sean and Jayden's expenses including their schooling, clothing, and insurance.

"There is nothing that Kevin has to pay for," the source explained. "Nothing has changed in the care Britney has given the kids and Kevin has acknowledged what a great mom she is." Unfortunately, as great of a mom as she may be, Kevin still wants more dough and he's going to put up a fight for it.

Kevin feels like he is entitled to more money because when they agreed on $20,000 a month in child support, he was still "relevant" in the DJ scene. It was 2008 and he was high in demand. Since he now reportedly only makes $3,000 a month, and Britney is on top of her game after finishing a residency in Las Vegas and planning to go on tour, Kevin thinks she should be coughing up more than the amount they originally agreed on.

The duo's whirlwind relationship started when they were first spotted together in April 2004. And just seven months later, Britney and Kevin were married. The pop star announced that she was pregnant with the couple's first child in April 2005. Sean was born on Sept. 15, 2005, and one year later on Sept. 14, 2006, their second child, Jayden, was born. Britney filed for divorce at the end of 2006, and it's been a bumpy road ever since.