Austria has said it is planning to construct a fence at the main border crossing used by migrants entering the country from Slovenia.
Austrian Chancellor Werner Faymann said the move would not shut the border, but would allow better control of arrivals.
It came as Germany said it expected the number of deportations of failed asylum seekers to rise.
Meanwhile, at least three migrants drowned and 242 were saved when a boat sank off the Greek island of Lesbos.
"We do not have a picture of how many people may be missing yet," a Greek coastguard spokeswoman said.
Earlier, three migrant boats were reported to have capsized between Turkey and the Greek islands amid worsening weather in the area.
BBC Europe correspondent Damian Grammaticas says Austria and Germany, the two countries at the heart of Europe's refugee crisis, seem to be toughening their tone.
They appear to be trying to deter refugees from setting out on their journeys and to head off political critics at home, he adds.
The UN estimates more than 700,000 migrants have crossed to Europe by boat so far this year - mainly from war-ravaged Syria. The approach of winter has so far done little to slow the flow.
The latest moves came after Slovenia said it could erect a fence along its border with Croatia if an EU plan agreed on Sunday was not implemented. It follows suggestions from Serbia, Romania and Bulgaria that they might begin building their own barriers.
Some 85,000 refugees have poured into Slovenia in the last 10 days, after Hungary closed its border with Croatia.
On Sunday, 11 EU states and three non-EU countries agreed to set up reception centres with another 50,000 spaces in Balkan countries, and send 400 guards to assist Slovenia within a week. But EU members have previously been slow to deliver on pledges of such assistance.
"If the situation worsens and the Brussels action plan is not fulfilled, then Slovenia has several scenarios prepared, including the installation of a fence guarded by forces," said Slovenian Foreign Minister Karl Erjavec.
Hungary has already fenced off its border with Serbia and Croatia, so such a move would, in theory, mean sealing off that route entirely.
Following a cabinet meeting, Austria's chancellor said a series of barriers would be erected at the Spielfeld border crossing with Slovenia, where several thousand migrants have been arriving every day.
The barriers would improve security, he said, but would be nothing like the hundreds of miles of razor wire fencing Hungary has put up along the length of its frontier.
"We want to be able to carry out controls on people, and for that one needs certain technical security measures," he told reporters.
However, in a joint statement later, Mr Faymann and European Commission President Jean-Claude Juncker said "fences have no place in Europe".
"President Juncker called on Chancellor Faymann to work closely together with the Commission and UNHCR to ensure that the 50,000 objective is reached as soon as possible, including by means of an Austrian contribution," the joint statement said.
Germany's Interior Minister Thomas de Maziere has accused Austria of transporting refugees to the German frontier at night, leaving them there unannounced.
He warned that Germany would start to deport more people who didn't qualify for asylum, and described as "unacceptable" the fact that Afghans now made up the second largest source of arrivals in Germany.
Large amounts of aid had been spent in Afghanistan, Mr de Maziere said, and Afghans should stay in their country.
Bottlenecks and tensions
Ahead of the rescue of 242 people off Lesbos, the United Nations refugee agency said two migrant boats had overturned near the Greek island of Samos on Wednesday afternoon, while another capsized close to the coast of Lesbos.
Some of the migrants on board the three boats were rescued, but about 10 people - including 4 children - are said to be missing.
The weather in the area has worsened in the past few days, with gale force winds and rain affecting the Aegean Sea.
Some transit countries have been seeking to limit the influx, leading to bottlenecks and tensions with neighbours.
Most migrants have been making their way to northern Europe - primarily to Germany, which is expected to receive up to a million asylum seekers this year.
A note on terminology: The BBC uses the term migrant to refer to all people on the move who have yet to complete the legal process of claiming asylum. This group includes people fleeing war-torn countries such as Syria, who are likely to be granted refugee status, as well as people who are seeking jobs and better lives, who governments are likely to rule are economic migrants.