Meat processing workers at food firm Vion in Cambuslang near Glasgow struck on Monday of this week over pay.
The action is the first of a series of planned walkouts.
It comes after the Unite union members voted by 92 percent for strikes.
Vion is the largest meat processing company in Europe. It tripled its profits last year. But is only offering workers a below-inflation 2 percent pay rise, plus some improvements in holidays.
This follows 2 percent the year before and a pay freeze the year before that. The workers get just £7 an hour.
Further strike dates are set to be named targeting key production periods over the next three months.