Kelsey Grammer's Wife Believed to Be Behind Rift With Daughter Mason

Kelsey Grammer's strained relationship with his daughter has been going on for years ... and TMZ has learned some people close to the family believe his current wife may be driving a wedge between them.

Sources with direct knowledge tell TMZ ... Kelsey and Mason Grammer's relationship has been strained for a long time, and they believe Kayte Walsh has contributed to the rift by failing to nurture a relationship with her stepdaughter.

We're told Kelsey tends to believe whatever Kayte tells him, and Mason has spent years trying to build relationships with both her father and stepmother. Our sources say Kelsey is close with his son, Jude, and they believe that's because Kayte doesn't feel threatened by him the way they believe she does by Mason.

One source tells TMZ ... "A daughter should never have to compete for a place in her father's life."

What's more, our sources stress the longstanding family tension is separate from Kelsey's alleged failure to acknowledge Mason's recent birthday.

As we reported ... Kelsey's ex-wife, Camille Grammer, blasted the "Frasier" star Monday for allegedly failing to call or text Mason on her 25th birthday, writing on Instagram that a daughter should never have to wonder whether her father remembers her birthday.

Camille also slammed Kelsey's parenting, saying fatherhood requires showing up even when the cameras are off.

Camille and Kelsey were married for 13 years before their highly publicized split in 2010.