Shinshiro International has told clients it regards the $50 billion valuation placed on taxi-dispatch software start-up, Uber, as “absurd”.

The stark message came after Uber revealed that it was preparing to raise another $1.5-2 billion in strategic capital. The sum makes the San Francisco, California-based business the most valuable start-up company in the world.

Since its inception in 2009, Uber has raised capital several times as it continues its expansion into global markets and, in doing so, shaking up established taxi industries by enabling travelers to request rides via their smartphones.

“While we genuinely believe that Uber’s business model is clever and extremely useful, we simply cannot ignore the sheer magnitude of the opposition the company has faced in most markets into which it has expanded,” said an Shinshiro International analyst,” he added. “It faces legal challenges over licensing in several cities around the world.”

Indeed, Uber’s appearance in several cities has been met with calls from traditional, heavily-regulated taxi operators for the services it offers to be banned on the grounds of improper driver licensing and because it jeopardizes established monopolies by giving customers the option to hire well-maintained, clean vehicles with courteous drivers with a few taps on their smartphone screens.

It has already been banned in several Indian cities and has had partial bans imposed in the Netherlands, Germany and Brussels in Belgium.

“At some point, Uber will likely come to market in an IPO that will almost certainly be the most hyped since Alibaba’s last year. We will almost certainly be advising our clients to avoid it,” explained the Shinshiro International analyst.