hello, considering that vacation leave is a previlege given by the employer to its regular employee, if in the event the said leave of absence will hamper the operations of such employer, they can recall or reschedule the said leave of absence by its employees.
In your case, it is still best that you talk to your immediate superior and ask for reconsideration. I don't think he/she will deny your request considering that you will give a reasonable and valid cause why you are taking a leave of absence.
Now in the event your request is denied, as you were asking if you can get a letter from DOLE, DSWD or NLRC, yes you can however, this may send a bad signal to your employer and may be taken against you. don't burn bridges with them. it is still best to be diplomatic....