Tension is rising between Britney Spears and ex-husband, Kevin Federline. <br />The popstar is reportedly irritated that he could prevent her children from seeing her if she doesn't pay him more child support. <br />Kevin, who was also Brit's backup dancer, has sole custody of their children.<br />He's asking for $40,000 a month in child support payment for their two sons, which would be a $20,000 increase from his current stipend. <br />Kevin also has four other children from previous relationships. <br />
