Okay, so this has been a great bother for me over the years. As a general rule of thumb, I usually follow this format: using "a" for singular and none for plural. Like so,
You do not need to take further actions.
And
You do not need to take a further action.
But I recently saw this sentence written in a TOEIC book. So should it be
"You do not need to take further action", "You do not need to take further actions", or both?
Action in this case will usually be used as a mass-noun, and that means that you do not count the actions.
You do not need to take (any) further action.
Compare that with similar sentences where mass-nouns are used:
You need to drink more milk.
There is no need to take offence at what she said.
Any further correspondence should be addressed to my lawyer.
As sugested by John Lawler's comment, grammar is not an issue in the following forms. All three are grammatical. All three express nearly the same core meaning: that further action is unnecessary.
You do not need to take further actions.
You do not need to take a further action.
You do not need to take further action.
Note, however, that the first two forms may sound odd to native speakers, because in the context of whether further action is necessary, action typically is used as a mass noun. It appears as a mass noun in the third form. Also note, the following forms might more commonly be used, unless there is reason to emphasize you:
No further action is necessary.
No further action is needed.
