Volunteers qualify for the incentive by creating a “grassroots fundraising” page through the campaign website and convincing at least five friends to contribute to Obama’s campaign during the promotion period, which began May 7 and ends Thursday at midnight.

Although the “official rules” do not recommend this, grassroots supporters who do qualify for the prize might want to make sure Mom is a registered Democrat before choosing to send tweets instead of a card. Winners can also direct tweets to another family member.

And for those who don’t qualify, the Obama campaign is now also offering free “Women for Obama” bumper stickers, as part of an ongoing push for the female vote.