Does this penalty apply even if you are doing a free action Multiple Attacks and dividing your dice pool among multiple targets?
With a burst fire weapon you have three options.
1. Aim at one target and tap the trigger once. This is the "Fire Semi-Auto, Single-Shot, Burst Fire or Full-Auto" Simple Action. The weapon will automatically fire 3 bullets. You resolve it as one single attack. Since the attacker is firing 3 bullets at the target, the target get a negative dice pool modifier of 2 dice to avoid getting hit.
2. Aim at one target and tap the trigger twice. This is the "Fire Long Burst or Semi-Auto Burst" Complex Action. The weapon will fire 3 + 3 bullets which will be resolved as one single attack. Since the attacker is firing 6 bullets at the target, the target get a negative dice pool modifier of 5 dice to avoid getting hit.
3. Aim at one target within short or medium range and tap the trigger once, then aim at a second target within short or medium range and tap the trigger a second time. This is the "Fire Long Burst or Semi-Auto Burst" Complex Action combined with a "Multiple Attacks" Free Action. The attacker need to have a weapon skill (not dice pool) of 3+ in order to attempt this. The attacker split the dice pool between the two attacks. Since the attacker is firing 3 bullets at each target, they both get a negative dice pool modifier of 2 dice to avoid getting hit.
For example a SA burst ...
With a SA weapon you also have 3 options.
1. Aim at one target and tap the trigger once. This is the "Fire Semi-Auto, Single-Shot, Burst Fire or Full-Auto" Simple Action. The weapon will automatically fire 1 bullet. Since the attacker is only firing one bullet at the target, the target don't get a negative dice pool modifier to avoid getting hit.
2. Aim at one target and tap the trigger three times. This is the "Fire Long Burst or Semi-Auto Burst" Complex Action. The weapon will fire 1 + 1 + 1 bullets which will be resolved as one single attack. Since the attacker is firing 3 bullets at the target, the target get a negative dice pool modifier of 2 dice to avoid getting hit.
3. Aim at one target within short or medium range and tap the trigger once, then aim at a second target within short or medium range and tap the trigger a second time, then aim at a third target within short or medium range and tap the trigger a third time. This is the "Fire Long Burst or Semi-Auto Burst" Complex Action combined with a "Multiple Attacks" Free Action. The attacker need to have a weapon skill (not dice pool) of 5+ in order to attempt this. The attacker split the dice pool between the three attacks. Since the attacker is only firing one bullet per target they don't get a negative dice pool modifier to avoid getting hit.