The Herald understands that the majority of those in custody are Chinese and Vietnamese nationals.
A source said that many of the suspects arrested yesterday are "unfortunate wretches who are being exploited by criminal gangs".
These gangs are both Triad gangs, whose powerbase is abroad, and Irish gangs who have moved into the cannabis growing industry in the last three years.
It is believed that gardai identified members of the Wo Shing Wo triad gang operating in Ireland. Wo Shing Wo is recognized as a major Chinese crime syndicate involved in drug trafficking, people trafficking, prostitution and gambling.
It is considered to be the largest triad operating in Britain and gardai believe that London-based members are trying to establish a foothold here.
The operation, co-ordinated by the Garda National Drugs Unit, was also looking for evidence relating to firearm offences and the handling of stolen goods.
In one instance, gardai executed a European Arrest Warrant under which a man is to be sent to Poland for trial for a serious assault.
At a growhouse in Fermoy, Co Cork, 800 cannabis plants worth €640,000 were found while a smaller growhouse was also raided on Henrietta Place in Dublin.
Most of the Chinese and Vietnamese people who work in the growhouses are living in Ireland illegally and often live and work in appalling conditions.
A recent sitting of Cork Circuit Court, in which three Chinese nationals were jailed for five years each for cultivating cannabis with a street value of over €800,000, gave an insight into how they are taken advantage of by gangs.
It emerged that the men -- all aged in their 20s -- had responded to a Chinese website advertisement for work and came to Ireland illegally, unaware the work involved illegally growing cannabis.
They lived at an industrial unit where they tended the plants, for which they were to be paid €350 a week.
However sources say that in some cases, the workers barely get paid at all and "live in truly terrible conditions with little food and under constant threat".
Garda figures show that €32m worth of cannabis herb and cannabis plants were seized up to May this year.