Especially since the '08 financial crash, many people have lost their job. However, don't assume your child support order will automatically go down.
File a Modification Petition
In NY, one only gets relief retroactive to the date of filing, so if you lose your job, file a petition for modification right away. You cannot get a modification if you either voluntarily quit or are fired due to misconduct.
Burden of Proof
On your petition, you have the burden of proving you lost your job thru no fault of your own. Thus, you must produce a notarized letter from your ex-employer confirming you were laid off, or other similar proof. You must ALSO prove you're making a diligent job search. You can generally only prove this by submitting a job search diary, comprising printouts & recordations of all your efforts to find work commensurate with your prior earnings. You should be aware that if you're completely out-of-work, the Court will generally require 30-40+ efforts per week. If you're working part-time, this may be reduced depending on your hours to 10-30 efforts per week.