Spears and Federline share sons Sean, 17, and Jayden, 16, who now live with Federline in Hawaii.
Federline's powerhouse attorney, Mark Vincent Kaplan, exclusively tells ET that the original child support agreement between his client and the pop star "did not allocate how much money was allotted for either child." Kaplan says Federline "is going to need to have the amount re-calculated because instead of having Jayden for 50 percent of the time, he has Jayden 100 percent of the time."
As a result of Federline having Jayden full time, Kaplan says "this would result in an increase because of the increase in expenses." Kaplan added, "We are going to try to work this out with Britney's attorneys, but if not, we will have to go through the judicial process."
As ET previously reported, Federline and his wife, Victoria, moved to Hawaii with his and Spears' sons -- Sean, 17, and Jayden, 16 -- earlier this year. Spears consented to the move back in May after Federline broached the topic earlier this year. Amid the devastating fires in Hawaii last month, a source told ET that Federline, his two sons and Victoria were not physically affected by the wildfires "because they live on one of the neighboring islands, where they moved two weeks ago."
"Everyone is doing great in Hawaii and they are very happy," Kaplan also tells ET.
Federline's intent to request an increase in child support payments comes nearly five years after he and Spears hammered out a plan that paid him some $40,000 per month in child support. Spears had previously been paying $20,000 per month. After striking that deal, a source told ET at the time that Federline and his team were "extremely pleased."
As ET previously reported, Spears has not seen her sons in more than a year.