Libby Chamberlain says she will honor her presidential pick, Hillary Clinton, on Election Day with more than a vote. She also plans to wear a pantsuit.

Ms. Chamberlain, 33, has also recruited thousands of others who are hoping to see the election of the first female U.S. president.

A private Facebook group she created dubbing Nov. 8 as “National Pantsuit Day” has drawn more than 600,000 members in two weeks. On the page, the invitation-only members trade stories about their admiration for the Democratic nominee and discuss plans to sport their own version of Mrs. Clinton’s signature campaign-trail attire.

“There is a literal pantsuit thing happening, which does involve shopping for some and rummaging around in closets for others,” Ms. Chamberlain said. “But so much more important is the idea that we can take this symbol of feminism and the struggle for equality and own it. Literally wear it to the polls.”

Republican rival Donald Trump’s backers are also seeking to show support for their candidate.