Word/phrase for a task that must be done in the current sprint

Some tasks are important but can be pushed off until the next sprint (period in which we add developments to software).

But some tasks are essential and aboslutely must be completed in the current sprint.

Is there a word or expression for these kinds of tasks (can be from other contexts as well)?

Example sentence:

Please classify these tasks as ____________ that must be completed by November.

EDIT: I know that in other languages the word "iron" is used to express the strict nature of the task. But I'm not familiar with a similar English expression.

Solution 1:

critical

ADJECTIVE

3.2 Having a decisive or crucial importance in the success, failure, or existence of something.

https://en.oxforddictionaries.com/definition/critical

Please classify these tasks as critical that must be completed by November.