Senator Lynn Ruane says she's "baffled" that any business or organisation would make a decision to put up anti-homeless structures outside their buildings.
She said it can make rough sleepers feel like "the very architecture of their own city" is rejecting them.
The independent senator was speaking after sharing a photo of hoarding erected outside a building in Dublin, preventing homeless people from using the doorway as shelter.
The Department of Education says it owns the building and leases it out to the City of Dublin Education and Training Board.
In a statement, the Department said the temporary wooden hoarding is to be removed today.
They’ve also contacted homeless services, adding that impacted individuals have been offered places in hostels.
On Newstalk Breakfast, Senator Ruane said one man has used the doorway in question as a shelter for a long time.
She said: "When I watched him seek shelter from that doorway I thought how safe he must feel in that community, and how settled he must feel there... not taking away from the fact that housing policy has failed for a long time, and people are in this situation in the first place."
However, the senator says this is not the first or only example of this happening in Dublin - with some other buildings have been installed with spikes or sprinklers to prevent rough sleeping.
She said: “When I see structures like this, it feels discriminatory. It’s like the very architecture of your own city rejects you.
"You’re already on the streets, homeless and needing support. You’re already needing to rely on the respect of other people to make sure when you’re at your most vulnerable, you’re still safe.
“For me, whatever about housing policy and addressing services… there’s also the very, very basic human decision that gets made to put it there that I’m always baffled by.”
The independent politician said Dubliners should be looking to make people feel more comfortable and more welcome, rather than "rejecting them even more".
She said the shops or organisations that install these structures are in a minority.
An argument that's been used in favour of such structures is that staff are left to clean up anything that may be left behind by a rough sleeper.
However, Senator Ruane says the likes of drug paraphernalia being left behind is not as common as people might think.
She said: "For me, if you have people who are seeking refuge in your doorway at night… you create a policy for that shop about how you manage it in the morning.
"You create connections with the services around you to ensure people are moved on.
“When they are in your doorway, what decisions are you going to make to make sure they feel safe and don’t feel further rejected or discriminated against?"
She also noted that not everyone feels safe in a homeless hostel, so may choose to sleep rough instead.