Hundreds of Greek dock workers staged a protest in Athens Wednesday against plans to sell most of the state's stake in the Piraeus port authority (OLP), which runs Greece's main harbour.
The government plans to divest 67 percent of OLP, from its current controlling stake of 74 percent.
However, unions say a sale to private investors will inevitably bring layoffs to the port authority's 1,100 staff.
"The government is in the process of kicking us out... we fear layoffs," said George Kelaidis, a member of the OLP union who has worked at the port for 26 years.
The Greek parliament is expected to approve the terms of the sale, which cover one of the port's three container terminals, a car terminal, cruise facilities and a repair dock.
OLP has a lease until 2052 on the infrastructure, which remains the property of the Greek state.
The other two container terminals at Piraeus are operated by Chinese shipping giant Cosco, which signed a 35-year concession for the facilities in 2008.
Piraeus is a key port of call on the Mediterranean Sea cruise circuit.
Overall, a dozen ports around the country including Thessaloniki are to be privatised under a state asset programme mandated by Greece's EU-IMF debt rescue.
Under the terms of the programme, Greece must raise 3.5 billion euros ($4.8 billion) in privatisation proceeds this year, and 9.5 billion overall by 2016.