From the ALA VLLD page:
Virtual Library Legislative Day is part of the American Library Association’s (ALA) National Library Legislative Day, held each spring in Washington, D.C. This year, National Library Legislative Day will be May 7-8, 2018.
Virtual Library Legislative Day activities will be held throughout the week of May 7-11, 2018, and will be an opportunity for all library advocates to make their voices heard on a national level.
Library advocates who cannot make it to Capitol Hill for the event can be a part of the effort by calling and/or emailing their elected officials any time the week of May 7-11.