It's pretty much like FFB said. It just depends on the airline. Not YOUR airline, the agreements YOUR airline has with the OTHER airlines. Some will allow your designated travel companion, some won't. Some will ONLY allow a "domestic partner", but no travel companion.

You have to either look at your company's agreement with the specific airline or simply ask the person in you airline's travel bureau.

Want to go to Australia with a friend and you don't work for a UEX carrier that allows a travel companion/buddy pass on UAL, or the ability to travel ID90/ZED with your friend? It's simple, you guys pool your money and buy your friend the CHEAPEST ticket you can, and YOU JS on UAL, Polar, or Atlas and meet them there.