Pencil only

I was emphatically told that I had to use the pencil provided in the booth; failure to do so would render my vote invalid.

Voting, then, is the only federal documentation of which I am aware that one can, leave alone is required to, fill out in pencil.

All other documents I can remember had to be filled out with indelible marker (either dark blue or black).

Is the value of my vote so low that it merits only impermanent inscription?