Robert De Niro speaks at the 20th annual Screen Actors Guild Awards in Los Angeles in 2014. (Frank Micelotta/AP)

Friday, April 20, is National School Walkout day, when students in schools around the country are expected to walk out to protest what organizers say is inaction by local, state and federal officials to take action to prevent gun violence.

It is the 19th anniversary of the killings of 13 people by two students at Columbine High School in Colorado, and the latest of several massive student-led demonstrations against gun violence since the Feb. 14 killings of 17 people at Marjory Stoneman Douglas High School in Parkland, Fla.

As a gesture to help students who are planning to participate, actor Robert DeNiro has penned an “excuse letter” for anyone in need. CNN confirmed with DeNiro’s representatives that the letter did indeed come from him.

Students in every state are expected to walk out of school at 10 a.m. local time and will gather for 13 seconds of silence to honor the 13 victims at Columbine. After that, students are asked to have discussions about gun violence and solutions, and then participate in events that have been planned by local walkout leaders.

The official website of National School Walkout has another excuse letter on it, this one from actress Julianne Moore:

The event was originally conceived by Lane Murdoch, a 16-year-old sophomore from Ridgefield, Conn.