Understanding Your Company's HR Policy
First, you need to read your HR policy manual or employee handbook to see what is allowed in your company.
Checking Organizational Structure
Second, you need to check out what your company's organizational structure is in terms of authority (to make decisions) and responsibility. These should tell you whether or not you are allowed to grant leave without the approval of your managers in the hierarchy above you. In case of doubt, send an email to your HR team and ask what you can and cannot do.
Company-Specific HR Policies
HR policy is not a generic document that applies across companies. It is specific to your company. So, you need to follow what your company has laid down.
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