A survey has found that over 60% of tenants reported difficulties getting their deposit back from landlords.
The survey was conducted by the Union of Students in Ireland in association with Red C.
The USI says there are a small number of landlords who are not registered with the Residential Tenancies Board and who are taking cash deposits actively targeting students.
The Residential Landlords Association says deposits are retained in only 0.1% of cases.
It said the USI survey is designed to drum up publicity for a deposit retention scheme, which it opposes.
A spokesperson for the Residential Landlords Association said it does not condone bad landlord behaviour.
However, Fintan McNamara said he was concerned that the results of the survey would result in the introduction of a "custodial deposit scheme", whereby the landlord will not hold the deposit but it will be paid to an independent body.
Speaking on RTÉ’s Morning Ireland, he said similar schemes have not been successful in the UK and there are better ways of dealing with landlords who do withhold deposits, such as by imposing fines.
USI President Annie Hoey said some landlords view students as easy targets and do not return deposits.
She also said some students were made wait by landlords, and were uncertain if they were going to get their deposit back.
"Very often students are transient groups and they don't have time to be staying around, waiting for this deposit to be returned, as they go off to work, on J1s..."
She said that while this situation is not representative of all landlords, there are some unscrupulous ones.
"This isn't representative of all the landlords in the country. I think we find sometimes unscrupulous landlords who don't register with the PRTB, that target students and then ... say oh this is broken or did you not know there was a cleaning charge".