Less than half of all tenants entitled to claim a new Rent Tax Credit have submitted a claim.
Many are citing issues with their landlord or being put off by engaging with Revenue.
The Rent Tax Credit is available for the tax years 2022 to 2025, and reduces the amount of income tax that people are due to pay for a tax year.
The maximum value of the credit is €500 per year for individuals or €1,000 for jointly assessed, married couples or civil partners.
Marian Ryan is Consumer Tax Manager with Taxback.com.
She told The Home Show people are interested in the credit.
"They want to claim it, but we're finding that the uptake in people actually getting to the point where they can get a refund is a lot lower than we had thought," she said.
"We estimate there's around 400,000 people in Ireland that are eligible to claim the Rent Tax Credit.
"So far less than half, about 190,000 claims, have gone into the Revenue in relation to it".
Ms Ryan said properties must be registered with the Residential Tenancies Board to avail of it.
"A lot of it is fear; so people are afraid to talk to their landlords to get the information they need," she said.
"When you're claiming the Rent Tax Credit for a private rental, you need to have your RTB registration number.
"A lot of tenants would need to contact their landlord to get their RTB registration number".
Ms Ryan said there can be a concern that the landlord is not registered with the RTB, but also "a lot of tenants have the fear of having any sort of a conversation with their landlord.
"They're afraid if they have a conversation with the landlord and say, 'What's my RTB registration number?' the landlord goes, 'Here's your number there and we have to increase your rent'.
"We're finding that a lot - and we're even finding people coming to us saying, 'My landlord increased my rent last September and now they're talking about increasing it again a second time'".
Ms Ryan said there are ways around having to interact with a landlord.
"If you are fearful of talking to your landlord about this, you can try and find your RTB registration number yourself," she said.
"If you go on to the RTB website, you can go in and search the register there for your Eircode that you're living in, and that will tell you whether that Eircode is registered or not.
"Then you contact them and say, 'Can I have my RTB registration number linked to me', and that means you don't have to have any conversation with the landlord," she added.
More information on the Rent Tax Credit can be found here