For the last four hours of the contest, which ends at 4 p.m. ET on Thursday, every time fans use the hashtag #BryceIn12 on Twitter, it will count as a vote.
Fans can follow @MLB on Twitter for the latest standings updates in advance of the deadline. At last count Thursday morning, the race had tightened but Harper still trailed St. Louis' David Freese for the top spot among the National League candidates. Atlanta's Michael Bourn and Arizona's Aaron Hill were third and fourth, respectively.
Yu Darvish remains in first among AL contenders.
Harper, who was 2-for-4 with two runs and a walk in the Nationals' 9-4 win against the visiting Giants on Wednesday, could join shortstop Ian Desmond and pitchers Stephen Strasburg and Gio Gonzalez to form the largest contingent of Nationals at an All-Star Game since the franchise moved to Washington in 2005.
"It's great. Having the fan support and whatnot, and really having them get going for me and vote for me, it's great," Harper said after the game Wednesday. "If I don't make it, it's OK. Hopefully I've got a few more tears to try to make the team. I think the fans are going to have a lot of fun up there. That's the biggest thing. It's for the fans. If I don't go, it's not going to hurt them at all."
Fans also can use their mobile phones to vote at MLB.com/vote or via text message. To receive the 2012 All-Star GameMLB.com Final Vote presented by Firestone mobile ballot, text the word "VOTE" to 89269. To vote for Harper, simply text message N3 to 89269. Mobile voting in Canada also is available and fans should text their choices to 101010. Std rates may apply.
The Nationals and Orioles are encouraging fans in the Washington and Baltimore area to get out and support both Harper and Orioles pitcher Jason Hammel, who joins Harper on the teams' combined "Beltways Ballot."
Fans can use #VoteHammel to support the Orioles' hurler in the American League campaign. This is the second successive year the teams have partnered for the Final Vote, as last year Adam Jones and Michael Morse formed the inaugural "Beltways Ballot."
The Nationals have had a player participate in the Final Vote balloting in each of the past four seasons -- Cristian Guzman in 2009, Ryan Zimmerman in 2010, Morse in 2011 and Harper this year. None of them won the contest.