Is there a word for "without any reason" but a more formal one

A sample sentence would be:

Why did you ban me without providing a reason?

Is there a single word to replace "without providing a reason" with? Indiscriminately is not an option for me.

Solution 1:

Unjustifiably comes to mind: a reason is needed to justify an action. Or possibly perversely. Or unreasonably.

unjustifiable : Not able to be shown to be right or reasonable

perverse : Showing a deliberate and obstinate desire to behave in a way that is unreasonable or unacceptable

unreasonable : Not guided by or based on good sense

^{_{Oxford Dictionaries Online}}

However, without providing a reason doesn't mean that there isn't one and the ban cannot be justified.

Solution 2:

Your action in banning me was arbitrary and capricious, you'll be hearing from my solicitors shortly.

Solution 3:

Consider gratuitously and unwarrantedly for "without any reason," and "unexplainedly" for without providing a reason.

gratuitous: being without apparent reason, cause, or justification.

unwarranted: without a basis for reason or fact; unjustified.

unexplainedly: without explanation.

^{Sources: Random House Dictionary, The Free Dictionary, Wiktionary}