Rihanna and Chris Brown Anger Fans with New 'Birthday Cake' Song

Rihanna has upset a number of critics after reportedly forgiving Chris Brown for assaulting her in 2009, and their renewed friendship has reignited speculation that she is considering leaving Jay-Z's recording label Roc Nation.

The 24-year-old singer, who is managed by Roc Nation, is scheduled to release "Birthday Cake" a song in which she recently collaborated with Brown, her ex-boyfriend who pleaded guilty to felony assault after seriously beating her in 2009, according to MissInfo.TV.

Rihanna and 22-year-old Brown's reconciliation has upset a number of people which reportedly includes her "mentor" Shawn "Jay-Z" Carter, who owns Roc Nation.

In September various media outlets, including 102 Jams radio and Blind Gossip, reported that Rihanna came close to leaving Roc Nation after feeling pressured by Jay-Z to cut ties with Brown to maintain her public image.

After Rihanna and Brown's recent "Birthday Cake" collaboration, Jay-Z along with a number of fans allegedly became furious which resulted in a defiant Rihanna reinstating threats about leaving Roc Nation.

A Billboard.com staff member known as, Jason Lipshutz, recently publicized an "open letter" to the Bajan singer which explains why he opposes Rihanna's reconciliation with Brown.

"The news about CB dropping by your 'Birthday Cake' remix… damn. Three years and nine days later, it is officially implied that, no matter if you two are 'single' or 'in a relationship' or 'it's complicated,' a token of forgiveness has been earned by Brown. And that's not cool, to a whole lot of people," Lipshutz wrote.

"Young girls look up to people like you to guide them through circumstances too complex for them to tackle on their own, and by granting Chris Brown an iota of tolerance, you implicitly encourage others to consider doing the same," he added.

Rihanna, who invited Brown to her 24th birthday bash on Monday night, is said to be unfazed by the growing concerns and took to Twitter to respond to critics like Lipschutz.

"I feel bad for that poor bandwagon...Trying its hardest to fit everyone," Rihanna tweeted on Friday. "Music heals the world...we need more!!!!" another tweet read.

"I'm so solid as a rock, they just can't stop me now!" she later posted.

A number of celebrities criticized Brown via Twitter on Sunday, after the "Kiss Kiss" singer performed at the Grammy awards and won a Grammy for best R&B album for his fourth album F.A.M.E.

"Not cool that we act like that didn't happen. He needs to listen to Gunpowder and lead and be put back in his place. Not at the Grammys," country music singer Miranda Lambert tweeted.

"Birthday Cake" is a song from Rihanna's latest "Talk That Talk" album, and is due for release on Monday.