You can do it multiple times, but the total can never be more than -3 in a single skirmish.
So the following combinations work:
1 card with 1 other
![Sauron [Sauron]](https://lotrtcgdb.com/forums/Smileys/classic/sauron.png)
Orc: -1 total
2 cards with 1 other
![Sauron [Sauron]](https://lotrtcgdb.com/forums/Smileys/classic/sauron.png)
Orc: -2 total
3 cards with 1 other
![Sauron [Sauron]](https://lotrtcgdb.com/forums/Smileys/classic/sauron.png)
Orc: -3 total
1 card with 2 other
![Sauron [Sauron]](https://lotrtcgdb.com/forums/Smileys/classic/sauron.png)
Orcs: -2 total
2 cards with 2 other
![Sauron [Sauron]](https://lotrtcgdb.com/forums/Smileys/classic/sauron.png)
Orcs: -3 total (not -4, because the limit is -3)
1 card with 3 (or more) other
![Sauron [Sauron]](https://lotrtcgdb.com/forums/Smileys/classic/sauron.png)
Orcs: -3 total
Of course you can always discard additional cards after this; they just won't have any effect.
For example, you could do:
5 cards with 2 other
![Sauron [Sauron]](https://lotrtcgdb.com/forums/Smileys/classic/sauron.png)
Orcs: -3 total