By Kathryn Dill

A small but growing number of employers have moved to observe Juneteenth, which commemorates the end of slavery in the U.S., as a company holiday.

Plans to observe the June 19 holiday have moved swiftly across corporate America in the weeks following the killing of George Floyd, with businesses ranging from Nike Inc. and Twitter Inc. to law firm Nixon Peabody LLP and Spotify Technology SA, announcing employees would have a paid day off. Target Corp. is closing its Minneapolis headquarters Friday and offered time-and-a-half pay for hourly employees who work. Best Buy Co. awarded employees a paid volunteer day that could be used Friday or another day this year and said Juneteenth would be a paid holiday in 2021.

Though Juneteenth has long been commemorated with family gatherings and community-driven celebrations, some employees in recent years have pushed companies to recognize the day. As of Thursday morning, a Change.org petition to make Juneteenth a national holiday had more than 300,000 signatures.

"The vast majority of employers who are making this decision now are responding to what's happening now and seizing this moment," said Lauren Romansky, managing vice president in research firm Gartner Inc.'s HR practice. A recent Gartner survey of 600 U.S. employees found that 64% said the recent protests and concerns about racial injustice had impacted their ability to concentrate on their work.

Although a handful of high-profile companies have announced plans to commemorate Juneteenth, they represent a fraction of businesses across the country. The day isn't a federal holiday, though 47 states and Washington, D.C., treat it as a holiday or a special observance. On Thursday, Republican Sen. John Cornyn of Texas said he would introduce a bill to make Juneteenth a federal holiday, as did a number of Democratic senators including Kamala Harris of California.

Martin Luther King Jr. Day, observed annually on the third Monday in January to commemorate the civil-rights icon, is a federal holiday. A 2017 survey from the Society for Human Resource Management found that 39% of U.S. employers close that day.

"If that [MLK Day] only has a 40% uptake, I can't imagine this is going to be significantly larger going forward," said Johnny C. Taylor, Jr., CEO of the Society for Human Resource Management, about Juneteenth. "You may see a one-year spike."

Providing employees a paid holiday can generate goodwill but can carry some financial cost. Some companies are making Juneteenth a permanent paid holiday, while others aren't or haven't made definitive statements about plans beyond 2020.

Ms. Romansky said some are opting to award employees an additional floating holiday -- days that are separate from vacation time and are used to observe a holiday for which the company doesn't close -- rather than observing Juneteenth specifically, in what she described as an attempt by employers to balance employees' individuality with a shared set of values.

Juneteenth's roots date to 1865 after the end of the Civil War, but observation of the holiday gained popularity outside Texas during the Great Migration in the late 19th and early 20th centuries. The day took on greater significance in the 1960s and later years through the Civil Rights and Black Power movements.

"African-Americans wanted to claim their pride and their histories," said Dr. Joanne T. Hyppolite, museum curator at the National Museum of African American History & Culture in Washington, D.C. "Juneteenth was one way to do that."

Growing up in Dallas, Valecia Battle looked forward to her family's annual Juneteenth gatherings, which often included a barbecue, an amateur softball tournament and the celebration of her older sister's birthday. During college, she says, the day evolved into an opportunity for personal reflection.

Ms. Battle, now a third-year associate at law firm Boies Schiller Flexner LLP in New York, usually returns to Texas to celebrate with family. This year, she sent an email to her managing partner suggesting Juneteenth become a firmwide holiday, but discovered the firm was already discussing the move -- and ultimately made it a holiday -- after recent social actions nationwide.

"For us to know that we're celebrating this thing, and then for it to feel uniquely black, it felt great for my firm to acknowledge something we'd already been celebrating for years, for decades," she said.

Other employers announced efforts to observe Juneteenth in lieu of granting a holiday. U.S. Bancorp will close its offices and branches at 1 p.m. In an email to staff, Amazon.com Inc. Chief Executive Jeff Bezos wrote that he would be canceling meetings Friday and urged others to do the same. General Motors Co. will stop its North American production lines and observe 8 minutes and 46 seconds of silence on each shift, representing the length of time that Mr. Floyd lay prone with his neck under the knee of Minneapolis police officer Derek Chauvin.

Some people say granting a holiday is little more than a gesture, arguing that American corporations still have much work to do to achieve racial equality. "Not that I don't believe that it should be, but I think these companies need to do more," said Jameeka Green Aaron, chief information officer of West Coast operations for United Legwear & Apparel Co. "We are lacking access to C-level positions and senior-level executive positions." United Legwear & Apparel is recognizing Juneteenth as a company holiday.

Carlos Moore, managing partner at a branch of The Cochran Firm in Grenada, Miss., said that while he typically sends a company email or posts on social media in recognition of Juneteenth, it has been a normal day of work for him. After a friend in New York told him her firm would close on the holiday, he reconsidered.

Mr. Moore then decided to make Juneteenth a permanent paid holiday at his law firm. All of his roughly dozen employees have also volunteered to participate in a community event featuring a cookout and poetry reading, he said. "If I'm going to be at a minority-led firm, and I'm the managing partner, I can close my office."

Write to Kathryn Dill at Kathryn.Dill@wsj.com