About 180,000 people, many fleeing war in Syria and Afghanistan, have entered Alpine state since mid-October
Trucks carrying wire fencing have arrived in the Slovenian village of Veliki Obrez, close to the border with Croatia, a day after the government said it would start erecting barriers to control the flow of refugees and migrants.
Large numbers of soldiers and police were drafted in, some guarding construction equipment, according to a Reuters photographer at the scene.
Slovenia is the smallest country on a major route for refugees and migrants heading north on their way to Austria and Germany.
About 180,000 people, many fleeing war in Syria and Afghanistan, have entered the Alpine state since mid-October, when Hungary fenced off its border with Croatia and pushed the migrant route towards its western neighbour.
The Slovenian prime minister, Miro Cerar, said on Tuesday the border would remain open, but the fence would help control the flow of people.
He said his country would not have the resources to shelter large numbers of migrants over the harsh winter if Austria shut its border, creating a bottleneck.
About 175 police officers from other EU states have come to Slovenia to bolster the local force, with another 100 expected in the next two weeks.