Strikes in Greece caused transport chaos and slowed hospital care and shipping Friday as workers protested against changes to a 36-year-old industrial action law demanded by the country's creditors.

Sailors and hospital doctors participated in the walkout, as did staff at the Athens metro, causing huge traffic jams in the capital as commuters used their cars instead.

Some 9,000 people were demonstrating in the city centre against the overhaul, part of a multi-purpose bill that will be voted on in parliament on Monday.

Leading union GSEE said the bill -- demanded by the country's creditors -- "deals a killing blow to workers, pensioners and teh unemployed...effectively eliminating even constitutionally safeguarded rights such as the right to strike."

The amendment to a 1982 law sets a higher worker participation requirement for strikes to be decided at primary union assemblies.

The participation threshold is raised to at least 50 percent of paying union members, from as low as 20 percent currently.

GSEE says the change will affect "99 percent of future strikes", though there is speculation that unions may find ways to bypass the new rules.

Around 50 general strikes have been held since the start of the Greek economic crisis in 2010.

Greece expects to draw 4.5 billion euros from its current bailout package after fulfilling its latest reform requirements.

The bailout agreement expires in August, whereupon Greece intends to finance its borrowing without a safety net for the first time in nine years.