Why are Kyle Richards and Kathy Hilton at odds?

What New Show Was Kyle Richards Referring To On 'RHOBH'?

Accordig to a new report, the sisters' dispute stems from drama between their husbands, who used to work together before Mauricio Umansky branched out on his own.

“Rick thinks Mauricio has created too much of a competition by breaking off with his own real-estate business,” an insider explained to Us Weekly on Saturday. “And Kyle won’t be anywhere near Rick and Kathy without her husband, understandably, so every family gathering is full of tension.”

New Details: Why Is 'RHOBH' Hubby Mauricio Umansky Feuding With Brother-In-Law Rick Hilton?

Most recently, Richards reportedly skipped out on a family Christmas party due to Rick's issues with Umansky.

“Kyle skipped the party because Mauricio wasn’t invited,” the source explained, "Kathy has always treated Kyle like a little sister and Kyle is just over it.”

In addition, claimed the source, Hilton isn't thrilled with Richards' decision to expose their family life in a new comedy series.

“Kathy was mad about Kyle signing the new deal for the show about her upbringing without consulting her,” the insider said.

Added a second source, "Kyle doesn't feel she needs to get Kathy's permission to tell the story of her own life."

For more of Kyle Richards and her family drama, tune into The Real Housewives of Beverly Hills season six, airing on Tuesday nights at 9 p.m. on Bravo.