If you're not getting paid, how are you an employee? If your only compensation is equity, that means that you're putting as much on the line as the co-founders, with an equal level of odds of getting a return on your commitment. In that case, your payout on the gamble should be, if not the same, at least comparable. If they're unwilling to offer that, then there needs to be a fair salary from day 1.
There is also no mention of how much of a track record the OP has in terms of creating success. Everyone is going on about how this is such a raw deal for him. If he has no real wins on his resume, this could be a huge opportunity to create something that he can take a lot of credit for, and leverage that to either co-found his next venture, or join an early stage startup with the ability to demand a good overall package.
Sometimes you have to actually take a less-than-optimal deal to build up a platform under yourself from which you can shout your next requirements from.
That's true of them as well.