Do you start the new job before you go away? If yes, you need to tell your line manager asap.
I can't think of any job that would be okay with you taking 2 weeks of leave at the very start where it wasn't pre-agreed at point of employment. They've hired you because they need staff, they will be co-ordinating rotas and expecting you to integrate into the team when you start. You may also have a probationary period, this is usually about 3 months and it's common for employers not to approve any annual leave in this time period. Have a look at your contract to see what their policy is for leave.