Some landlords in Dublin are demanding prospective tenants pay two months rent as a deposit.
The standard request is for homeowners to ask renters for a month's rent upfront and one month extra as security.
However more landlords are looking for higher lump sums to mirror what their counterparts in the institutional sector are doing.
Labour TD and former Minister for Housing Jan O Sullivan is calling for the process to be stopped immediately.
"The Residential Tenancies Board has the power to intervene in these kind of disputes. If (landlords) are looking for two months deposit as well as the first month's rent, I'm not sure that's actually legally allowed. I think there could be ministerial intervention if that's needed to stop this."