Federline's lawyers have blocked plan for boys to stay in home bases near Circus stops, TMZ claims.By Gil Kaufman Britney Spears Photo: Getty Images She's got a hit album that just went platinum, is about to release her third single and has a sold-out tour in the works. But, according to TMZ, Britney Spears has threatened to cancel her upcoming Circus tour if ex-husband Kevin Federline's lawyers insist on blocking an agreement that would allow her to take the couple's two sons on the road with her. Citing unnamed "informed sources," TMZ reported that for several weeks, Britney, her father, Jamie Spears, and K-Fed have been privately working on a plan to let Sean Preston and Jayden James travel with the singer while she goes on the 33-date tour. According to the plan, Britney would have three home bases while on tour — in New Jersey, New Orleans and Los Angeles.