Most federal offices, such as the US Postal Service, are closed during Juneteenth. Markets like the Nasdaq and New York Stock Exchange don't trade during the holiday, either.
But whether private companies and state governments remain open varies. Most major banks are closed for the holiday, but not all companies provide paid time off.
The White House press office didn't immediately respond to Business Insider's request for comment regarding Trump's Truth Social post.
Earlier on Thursday, White House press secretary Karoline Leavitt said at a press briefing that the White House was open. When asked by a journalist about commemorating Juneteenth, she said she was "not tracking" Trump's signature on any proclamations for the holiday.
"I know this is a federal holiday," she said. "I want to thank all of you for showing up to work. We are certainly here. We're working 24/7 right now."
Trump himself supported making Juneteenth a federal holiday in the wake of widespread protests following the killing of George Floyd. "Make Juneteenth a National Holiday" was included among his "Promise to Black America over 4 years" policy proposals in his 2020 presidential campaign.
During that campaign, Trump took credit for publicizing Juneteenth after moving one of his rallies from June 19 to June 20 in Tulsa, Oklahoma.
"I did something good: I made Juneteenth very famous," Trump told The Wall Street Journal at the time. "It's actually an important event, an important time. But nobody had ever heard of it."
In the same interview, Trump expressed surprise that his administration had commemorated Juneteenth every year.
"Oh really? We put out a statement? The Trump White House put out a statement?" he said, according to the Journal. "OK, OK. Good."
The White House did not publish a statement on its website commemorating Juneteenth this year.