The US Army's missile testing range on the Marshall's island of Kwajalein is restricting access for Marshallese workers and other visitors to the base.
The move is aimed at halting drinking problems among Marshall Islanders and to comply with tightened Army regulations to comply with US Homeland Security.
From tomorrow, workers must be through the check point at the Kwajalein dock within one hour after their work shift ends.
A similar system was in place prior to 2001, but it had been relaxed to allow workers to stay on the island for up to three hours after their shift finished.
About 12,000 Marshall Islanders live on the over-crowded island of Ebeye, a three-mile commute by boat from Kwajalein.
About 3,000 American workers and their families live on Kwajalein Island.