"We haven't been able to reach our family members since noon Monday after an attack by Daesh on the factory," said a resident of the town of Dmeir, 50 kilometers (30 miles) east of Damascus.
"We have no information about where they are," the resident added.
An administrator at the plant said 250 employees had been unreachable since Monday.
The so-called Syrian Observatory for Human Rights said "dozens" of staff were believed to have been seized by Daesh from the cement factory and taken to an unknown location.
The Badiyah cement factory lies outside Dmeir, which has seen fierce fighting in recent days as government forces have shelled Daesh positions inside the town.
A Syrian security source told AFP that Daesh militants had also tried to seize the nearby Dmeir airbase and power plant from the government but had failed.