Not sure, but it's in the contract, if I remember correctly.
Also if you search that here, you'll probably find an answer in a thread somebody else made on this topic. I'm sure you can't be the first person to ask this.
Sorry I couldn't be of more help.
Also I asked you a couple questions in your thread about your grievance on back pay for delivering grounds as an air driver, if you could answer them when you get a chance I'd appreciate it.