As he delivers his last State of the Union speech on Tuesday, before a Congress that opposes new firearms restrictions, President Obama plans to highlight the impact of gun violence by leaving a seat empty in the first lady's box.

Obama told over 20,000 grass-roots supporters Friday, in a conference call, that there would be an unoccupied seat in Michelle Obama's box "for the victims of gun violence who no longer have a voice – because they need the rest of us to speak for them," according to a White House official in an emailed statement.

"To tell their stories. To honor their memory," the statement continued. "To support the Americans whose lives have been forever changed by the terrible ripple effect of gun violence – survivors who’ve had to learn to live with a disability, or without the love of their life. To remind every single one of our representatives that it’s their responsibility to do something about this."

The decision to leave a seat empty during the president's speech is not unprecedented: There was one in first lady Laura Bush's box in 2003 that symbolized "the empty place many Americans will always have at their tables and in their lives because of the attacks on Sept. 11, 2001," according to the White House at the time. That decision came in the run-up to the invasion of Iraq.

Obama's move is more confrontational, given many lawmakers' resistance to his plan to require occasional firearms sellers to obtain federal licenses and conduct background checks on potential purchases. But it is the latest example of how he is using the one tool he has left — the bully pulpit — to make his case for gun control to the American people.