The European Union has urged Greece to take specific steps to check the flow of asylum seekers to its shores and protect the 28-nation bloc's external border.
The European Commission adopted a draft report published last week that said Greece had failed to protect the EU's external frontiers from the continent's biggest influx of refugees and migrants since World War II.
The EU's executive arm on Monday recommended Greece improve registration procedures, including making sure migrants are properly fingerprinted and their documents checked against various security data bases.
It also urged Greece to properly accommodate asylum seekers while they are registered, work towards deporting economic migrants who cannot be classified as refugees, and improve border surveillance.
If Greece fails to comply with the recommendations, Brussels could authorise EU member countries to exceptionally extend border controls within the Schengen area - including with Greece - for up to two years.
The Schengen area allows passport-free travel through 26 countries, most of them in the European Union, and is held up as one of the major European achievements.
"Our ability to maintain an area free of internal border controls depends on our ability to effectively manage our external borders," EU Migration Commissioner Dimitris Avramopoulos said in a statement.
"Today we are proposing a set of recommendations to ensure that, at all external borders of Greece, controls are carried out and brought in line with Schengen rules," he said. "We will only save Schengen by applying Schengen."
The Commission specifically asked Greece to provide enough staff and fingerprint scanners to register migrants, as well as check their travel documents against Schengen Information System, Interpol and national databases.
"Border surveillance should be improved, including the establishment of a risk analysis system and increased training of border guards," the Commission said.
Last week's damning report said Greece faces border controls with the rest of the Schengen passport-free zone in three months if it fails to act.