"Selena has chosen Justin over her family in the past," a source told People. "They are disappointed about that.
"Her father has told her he doesn't like her spending time with him," the insider added.
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Although they have not yet confirmed they are back together, Justin and Selena have made no secret of their reunion.
After kissing over breakfast in Texas on Friday, Justin dedicated a song to Selena during his appearance at the South by Southwest (SXSW) Festival on Sunday. "The next song goes out to me baby," he told the crowd, before launching into his hit song As Long As You Love Me.
And this week, the 20-year-old posted a video on Twitter showing the pair dancing provocatively in a studio to John Legend's Ordinary People.
It's not the first time that Justin and Selena has rekindled their romance since their initial split in November 2012. In January, they were spotted riding Segways together, and Justin later Instagrammed a picture of them hugging, which he captioned, "Love the way you look at me."
But it is the first time they have reunited since Justin's recent arrest for DUI and subsequent run-ins with the law.
Selena's family are said to be increasingly concerned over his behaviour — a video has just been released of the pop star acting defiantly and swearing at his recent deposition — and are unhappy about the couple's decision to get back together, particularly given that Selena only recently left rehab.