Jenny Rathbone said some tenants were charged ??150 to have properties taken off the market while a contract was finalised, while others charged ??65 for cleaning the property.
The Cardiff Central AM called for a ban on the charging of such fees.
Ministers have warned of a risk that banning fees would push up rents.
In Scotland, all charges to private tenants other than rent and deposits have been deemed illegal since 2012.
Campaigners have called for similar rules in other parts of the UK.
In a Senedd debate, Ms Rathbone said: "It should be the landlord paying the letting agency, not the tenant."
She added: "Frankly, the letting agencies are getting away with simply not providing a service in exchange for the fee and I think it's something that needs to be stopped as a matter of urgency."
Assembly lawyers have told Ms Rathbone that Wales had the legal powers to impose a ban, despite the Welsh Government previously saying it did not have the authority.
Communities Secretary Carl Sargeant said agents were legally obliged to advertise fees, and he was "not persuaded" a ban was needed at this time.
"I wouldn't want to see the fees - extortionate fees in some cases - just being transferred to the tenant [in the form of higher rents]," he said.
"I would like to learn from the evidence from the experience in Scotland before deciding whether this measure is necessary," Mr Sargeant added.
Sunday Politics Wales is on BBC One Wales on Sunday 16 October at 1100 BST
Students and other people renting their homes have been victims of "widespread abuse" of fees charged by letting agents, a Labour AM has claimed.