wiggy
Don't do it. In the 1990's my employer wanted to impose such a system. Just don't sign, you can't be fired for that. I survived 10 years asking the co for a cash advance every trip. No fuel, so what? They'll change their mind fast.
You are not alone, make sure your colleagues are aware of the dangers.
When I was a 25 y-o new boy I was given a company American Express. The idea was that if I could be trusted to represent the company abroad I could be trusted with their card.