In a bid to get people to call and support Rob on the US TV show, the 31-year-old tweeted the number they needed to call, while pretending it was her friend Bieber's number.
She wrote yesterday: 'OMG I have @JustinBieber 's phone #!!!! 800 8683402! CALL HIM! He's taking calls for the next hour!!!'
Fans were quick to criticise Kim for the move.
She later apologised for her joke, writing that she had really been asking them to vote for Rob.
The reality star said: 'Ok guys obviously I'm joking, that's not Justin's #!
'But seriously call & vote for @RobKardashian & @CherylBurke 800 8683402!!! Xoxo'
Rob has been doing quite well so far on Dancing With The Stars, and last night he and dancing partner Cheryl Burke performed a cha-cha to Walk Like An Egyptian.