This is the 8485th most frequent Russian word.
несправедливо
Unfairly.
The word "несправедливо" is used here as an adverb to describe an action that is unfair or unjust.
Это было совершенно несправедливо по отношению ко всем студентам.
It was completely unfair to all the students.
"Несправедливо" functions as an adverb to express the manner of the action (the firing), emphasizing injustice.
Она чувствует, что её уволили несправедливо.
She feels that she was unjustly fired.
Here, the related root "несправедливое" is an adjective describing the noun "решение" (decision) as lacking fairness.