Can you not work until they're paying you or just get reimbursed later?

You should seriously talk to someone about how this can get fixed. You shouldn't be working for free. Talk about possibly being reimbursed for the work you're doing.

Talk to your boss or supervisor and try to fix it before they make you work on something big and not get paid for it.

then dont work.

They have no right to make you work without pay. You shouldn't technically have to work until they technically hire you. I mean no offence, but I hate the word technically. GAAH, tiny brother uses it for everything. "Technically, I didn't feed your lunch to the dogs, it fell" "Technically, I've only spent 7 hours on games today. TV doesn't count." Hope you enjoyed the rant. If not, get a milkshake.

I hope they can back-date your pay, otherwise that's technically slavery!

This is fundamentally asinine. They need to technically hire you or you need to technically leave.

If you're technically not hired, then you technically have no job which means you technically are not obligated to do any work. If you really want the job then you should get something in writing that states you'll be paid for the work that you did, even if you don't get hired, assuming they'll be benefiting from it. Otherwise, you might end up getting screwed over because you'll have done the work for them and then they can easily claim you're not an employee, etc. and not properly compensate you, or hire you in the end.

Document everything! You are working there, and went through the process of being hired. They will have to legally pay you. Don't fall for them saying they don't! It's their fault, not yours, for those technical issues.

Seems legit. </sarcasm>