COVID-19 health passes became mandatory for all workers in Italy from Friday (October 15).
But the measure didn't go down well everywhere.
At the major port of Trieste some labour groups had threatened to block operations in protest against the rule.
The situation appeared largely calm, with some workers demonstrating:
"The Green Pass is a bad thing" said one protester.
"It is a legalized form of discrimination, nothing else. It's not a health regulation, it's just a political move to create divisions among people."
Prime Minister Mario Draghi's cabinet approved the rule last month.
It makes it obligatory from October 15th for all workers either to show proof of vaccination, a negative test or recent recovery from infection.
But an internal government document seen by Reuters shows some 15% of private and 8% of public sector workers have no Green Pass.
Under the new rules, effective until year-end, those without the certificate will be suspended without pay.
And face a fine of up to 1,500 euros, or $1,700, if they try to work on regardless.
The government hoped the move would convince unvaccinated Italians to change their minds.
Over 80% of people over the age of 12 are already fully inoculated in the country.