Landlord tax

Ive just recived a letter from HSE about a guy i jave living in my house as he pays his rent with rent allowence 350 a month.
The HSE want my prsi number, will i have to pay tax on income i get from this 1 guy as i have not yet paid any and he been here 2 years, if i do will i have to pay back tax.
Are you allowed to make so much from rent income before you pay tax.

All help advice most welcome.

When you say he lives in your house, do you mean he lives with you in your own principal private residence?

If so then you have no real problem, see info re rent a room relief here: http://www.citizensinformation.ie/en/housing/owning_a_home/home_owners/rent_a_room_scheme.html

I believe you have to declare it on your tax return.

If it's under the Rent a Room scheme threshold then you are exhempt from tax on that income.