What it does
"Suppressing Fire" isn't an official Magic keyword or ability—it doesn't appear on any printed card or in the comprehensive rules. You may be thinking of a card from another game, a custom/proxy card, or confusing it with a similarly themed effect.
If you encountered this on a card in your playgroup, it's almost certainly homebrew or unofficial. Magic does have plenty of "deal damage to tap down or punish attackers" effects—things like pinging creatures, Goblin Sharpshooter, or cards with "deals damage equal to..." triggers—but none use that exact name.
For Commander specifically, double-check the card's actual name and Oracle text via Gatherer or Scryfall before building around it, since unofficial cards won't be legal in sanctioned play and may have ambiguous wording your table needs to agree on.
Iconic cards with Suppressing Fire
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