Grandparent post was in management, higher management wanted one of his reports disciplined for using the unlimited time off (in an amount that's not uncommon for anyone in management or with 5+ years at the company to have as vacation)

It means to talk to them in a stern way about something they did wrong.

https://www.vocabulary.com/dictionary/take%20to%20task

I didn't even get the 'report' part. Thanks all.

Parent is a lead/manager of some sort, and they were directed to verbally discipline a person who "reports" to them (IOW, works under parent commenter's org).

Someone who reports to the poster took three weeks off and the powers that be wanted the poster to have a "talk" with that person.