Many paranoid companies will often prohibit all use of GPLv3 software. The justification I've heard is that the terms of the license make it possible that anything you produce using GPLv3 software is also GPLv3. So, for example, if you use a GPLv3 licensed version of emacs, and you write some code, the code you wrote will also become GPLv3. It's a very conservative reading of the terms of the license, but understandable for companies which have most of their net worth tied up in source code.