The Japanese city of Iwakuni is voting in a referendum on Sunday on whether to accept plans to expand a local US marine base.
Though non-binding, the vote has become a symbol of local opposition to the restructuring of US forces in Japan.
The re-organisation, which will reduce overall numbers, was agreed by Tokyo and Washington in October.
Nearly 2,000 residents of another city, Zama, protested on Saturday at plans to boost US troop numbers there.
About 300 troops would be added to the 1,150 already stationed in the city just south of Tokyo.
The protest was backed by the city hall, local lawmakers and community associations, Zama city official Fumie Takahashi told The Associated Press.
"Residents in cities with US bases have been under various burdens for a long time for the sake of national defence," the organisers said in a statement.
"We ask the central government to fully respect the will of local residents."
Local feeling
The US proposes relocating a naval air wing, or 57 planes and 1,600 personnel, to its base in Iwakuni, a city 720km (450 miles) south-west of Tokyo.
Voters will be asked whether they support or oppose the plan.
If turnout is lower than 50%, the vote will be cancelled.
Mayor Katsusuke Ihara called the referendum after consistently opposing the expansion of the base.
"Just because the national government has decided something doesn't mean we must refrain from expressing our views," he said.
Local concerns include the noise level at the base.
The issue of US troops in Japan is also sensitive because of a case in 1995 in which three American servicemen raped a Japanese schoolgirl in Okinawa.