The Head of the media office of the General Association for Oil and Gas Workers, Mohamed al-Hosny, told Efe over the phone on Sunday that large numbers of the syndicate members joined the strike but gave no further details on the exact figure.
On Saturday, the syndicate announced the strike "in solidarity with the protesters."
Demonstrators in the southern Iraqi city of Basra burned tires and blocked roads, while governors of the cities of Babylon, Dhi Qar, Maysan, and Wasit declared Sunday a public holiday.
A civil servant from Babylon, named Zaynab, told Efe that she had not gone to work, adding she decided do so in solidarity with the protesters.
Parliament member of al-Sadr-led Saairun Alliance Salam al-Shamry described in a statement the Shiite cleric's call for a voluntary strike as an important step to support reform and change.
"The government should speed up implementing the demands of the peaceful demonstrators and all Iraqis in reforming and fighting corruption and its symbols," al-Shamry added in a statement.
"Or else, there are other peaceful ways to put things in the right place."
Demonstrations erupted on 1 October and spread through the capital and other regions of Iraq due to outrage over the lack of public services and employment opportunities.
At least 320 people have died and over 15,000 others have been injured, including members of the security forces in the ongoing unrest, according to figures issued by the Iraqi High Commission for Human Rights.
( With inputs from IANS )