A national organization promoting Sept. 11 as a day of public service and remembrance is asking presidential candidates to stop campaigning and running political ads on the 15th anniversary of the terror attacks.

The New York-based nonprofit, 9/11 Day, has sent letters to Hillary Clinton and Donald Trump.

It's also urging people running for Congress to refrain from campaigning on Sept. 11.

The nonprofit's president and co-founder, David Paine, says a one-day campaign moratorium would help revive the spirit of national unity and empathy that followed the attacks.

Representatives for Trump and Clinton did not immediately say whether their candidates would agree to a campaign moratorium.

The organization made a similar request in 2012. Both Mitt Romney and Barack Obama complied.