The route and timing of the demonstration, meant to protest pandemic restrictions in the United States, was set to be announced on Tuesday evening, said Brian Brase, a trucker who is organizing the American effort. According to messages posted on social media, the route may start in Sacramento, Calif., and end in Washington, D.C., but Mr. Brase declined to comment on details of the convoy until an official announcement was made.

It is unclear how large any such convoy might be, should it come to pass. But anti-vaccine activists have started planning on popular forums on Facebook and Telegram, the messaging app.

On Facebook, the hashtag #TruckersConvoy2022 has garnered almost 2 million interactions over the last two weeks, according to CrowdTangle, a data analytics tool owned by Meta, Facebook’s parent company. Private Facebook groups dedicated to the convoy have also seen fast growth, with the main group collecting nearly 150,000 members since it started two weeks ago. A second group, dedicated to the efforts in the United States, has gained 50,000 members in the last week.