Rulings

• 2014-02-01
  Unless some effect explicitly says otherwise, a creature that can’t attack you can still attack a planeswalker you control.
• 2007-02-01
  In the Two-Headed Giant format, you still only have to pay once per creature.
• 2004-10-04
  The payment is made during the declare attackers step at the same time you are declaring the attacker.
• 2004-10-04
  If there is more than one Propaganda on the battlefield, the cost is cumulative.
• 2004-10-04
  If there are multiple attacks in a turn, then you have to pay for each attack.
• 2004-10-04
  Paying this cost is not an instant or any other kind of ability, it is an additional cost on the declaration of the attacker.
• 2014-02-01
  Unless some effect explicitly says otherwise, a creature that can't attack you can still attack a planeswalker you control.