Your school just broke the contract. This is he biggest part of it. They paid you late. You get less interest now. They get more. They broke the contract. Feel free to also break it now. But of course they will be angry if you do.
This is a joke, right?
He actually can take them to the labor board, but it would just get him his money and then he would probably be the first person dismissed by his MOE under the '6 month probationary employee' rule.
@ OP: The bureaucracy in korea sucks. There can be so many reasons for not being paid on time. I will list them for you (and my list won't even be complete):
IN YOUR ADMIN. OFFICE
1. they forgot
2. someone is new and doesn't know their ____ from their____.
3. they didn't receive the correct bank information from you or your co teacher.
4. They paid the last person accidentally and are scrambling to get the money back (yes I have read about it happening on here or on Dave's)
At your MOE
1. They haven't sent over your pay for the quarter. (MY MOE gives my school 4 months worth of my pay and they pay me out of that, as well as paying off my rent, etc.)
2. MOE hasn't received your banking information or some other random form that should have no effect on your pay but does because this is Korea.
3. Depending on your district, they really have gotten their funds that were earmarked for you not given to them. This has been happening in the GEPIK area apparently.
There can be so many reasons, but it seems like you have a viable solution. Tell them today, if you read this before everyone goes home or tomorrow that you will contact your EPIK and/or MOE/POE representative and tell them the school has not paid you. If the money isn't in your account a day later call the reps. tell the reps. that your school is very unprofessional, you haven't been paid, etc. and you thought this would happen in japan but not korea. If the money is not in your account the next day then..... post a message on this forum and get some advice for your next step. Make it very clear to these people that getting paid on time is important to foreigners. It could be a one time error, so don't flip out yet.
If there is something fishy going on, PM me and I can teach you how to become a 'toxic employee'.