CAT FIGHT?! Taylor Swift Gives Katy Perry An Ultimatum!

There’s a storm brewing between Katy Perry and Taylor Swift — and one of their colleagues is caught smack dab in the middle.

An entertainment insider tells Radar Online that both singers have been using the same concert tour director and production designer, Baz Halpin, for years.

“Baz did Taylor’s most recent RED tour and the Speak Now tour, and he did California Dreamz and the current Prism tour for Katy,” notes the source.

And now that Perry, who will celebrate her 30th birthday on October 25, has scored the high-profile Super Bowl XLVIV Halftime Show, she’s asked Halpin to design it. “He’s working out the money details right now, but it’s obviously a huge career highlight for him and he wouldn’t pass up the chance to do it,” says the insider.

That dedication to Perry isn’t exactly sitting well with 24-year-old Taylor. “She got word of Baz agreeing to do the show for Katy and Taylor’s flat out said she will not hire him ever again for any performance or tour if he goes ahead with his decision.”

The insider says that Halpin would “be nuts not do the gig” and there’s no way he’ll pass it up.

As for Perry’s thoughts on the subject? “Katy got word of Taylor’s ‘ultimatum’ and found it quite amusing.”