The Bride Wars actress is guest starring in six episodes of the hit TV show's fourth season.
A source told US Weekly: "Kate says Lea is a nightmare. Once, during a technical delay, Lea snapped her fingers and said, 'Let's go. I have plans!'
"Kate's keeping her distance."
However, Michele's spokesperson insisted that the two actresses are getting on.
A representative said: "Lea has had a great time with Kate."
Sarah Jessica Parker also has a stint on Glee this season. Network Fox has vowed that the show is 'poised for a creative renaissance' as ratings dropped substantially last season.
Entertainment president Kevin Reilly explained that Glee will become a 'show within a show'.
Watch first-look video for the new season of Glee below: