Dear unknown Colleague

[lorean]

An invisible invader has taken the world
They call upon you to fight in the battle
They say you are an “integral” part of the group.

This first stanza is in the present-tense as opposed to most of the poem being in the past-tense. I would change this to match the rest.

But unlike any Soldier in the war,
you are without a gun
Working under egregious condition.
...
And yet, you continue to move heaven and earth.

Same thing with past/present-tense here. 

With no further ado, in the front line you stood and fought against the worst enemy

Instead of "With no further ado," I would say something like "Without hesitation." It feels more like what you're trying to convey, but I could be wrong.