Rebel sniper

Rebel Snipers are counter-infantry units in Halo Wars.

Background
Rebel Snipers are normally seen protecting Neutral Rebel bases. They are in teams of two and often have one star veteran levels. The Snipers can take out any infantry unit very quickly, even Spartans. However, they are not so effective against large groups of infantry or anything more powerful, like a warthog or tank.

They are also seen protecting garrisoned bonuses, sniper towers, etc. They give cover fire for standard Rebel Infantry.

They appear to be the rough equivalent of Jackal units.

Strategies
Early in the game, it is beneficial to take out groups of Rebels for the supply crates that appear when they are neutralised. If you are using infantry yourself to fight them, then upgrade some of their features, or bring some vehicle and/or air units along with them.

Also, in addition to upgrading marine features, using large groups of Marines could help take out these infantry killing threats. Take into consideration that the snipers pause to acquire new targets, and use this opportunity to use your main infantry's special ability to take out the snipers for good. Make sure all your units are not focusing on just the snipers, have some units attacking the snipers while others attack Rebel squads, capture structures, or destroy Rebel base turrets.

Air units are also effective at taking out these Rebel snipers. Take a group of Hornets to along to assist your ground forces with the Rebel threats. Scorpions with the Canister Shell upgrade are very effective to take out these snipers usually one shot from the canister from just one should take out both snipers.