Sweden is imposing identity checks from Monday on all those travelling from Denmark by train, bus or ferry in a bid to reduce the flow of migrants and refugees into the country.
The move has been sharply criticized by rail and ferry operators, who are responsible for checking the identity papers. They warned of high costs and longer travel times.
The checks will affect commuter and other trains on the Oresund rail and road bridge, which links the two Nordic countries, for the first time since the 1950s.
All train passengers in Denmark will be checked at Copenhagen airport train station, the last stop before the Oresund bridge. In the future, no trains from other stations will be allowed to enter Sweden.
Sweden says about 160,000 people applied for asylum in 2015.