A two-part assault on problem properties in the city of Pittsburgh starts with a mailer going out today, leading to registration of rental properties and enforcement of rules for disruptive property starting next month.

The mailer advertising the new rental registration system will go to every known city property owner, but only landlords need to pay attention. It lays out the procedure by which they have to register and pay $12 for each unit they rent out, by April 1, or potentially face fines of $1,000 for each unreported apartment or tenant-occupied house.

That's meant to improve building code enforcement, said Joanna Doven, spokeswoman for Mayor Luke Ravenstahl.

"We will know our property owners, we will know who they are, we will know where they live," she said Friday. "We're trying really hard to make it easy for people to register."

Representatives of landlords say there are a lot of questions about how the registration process will work -- and they're not thrilled about the cost.

"We feel that there are some issues in it that require a whole lot of duplications of things that a lot of landlords do already," said Tony Mete, president of the Realtors Association of Metropolitan Pittsburgh. "It's no big deal to somebody who owns a few properties, but if I own four buildings that have 100 units each, [then $12 per unit] is a lot of money."

He said his association may go to City Council to ask for changes.

As outlined in the city's brochure, landlords can register online starting Dec. 1 at www.city.pittsburgh.pa.us/bbi, or they can call 412-255-RENT to get the form mailed to them. They can mail in or drop off a check or money order, or, beginning in mid-December, pay with a credit card online.

One potential problem: Landlords need to send in a copy of their building's certificate of occupancy with their registration. If a building doesn't have a certificate of occupancy that matches its use and number of units, it will need to be inspected and brought up to code before it can be registered and rented out.

That could mean a rash of requests for new certificates of occupancy, taxing the already-strapped Bureau of Building Inspection staff.

"We'll have a little more demand on our inspectors this year," said Sergei Matveiev, chief building inspector. The ordinance requires that the registration fees be placed in a trust fund and then spent on building inspection if needed.

For those landlords without one, getting the certificate of occupancy "might be simple, and it might be very complicated," depending on how far out of compliance the building is, Mr. Matveiev said.

The city doesn't have enough staff to knock on every door to determine whether it's a rental or owner-occupied unit, Ms. Doven said. So $1,000 fines for failure to register will probably only kick in when an inspector or community group notices that a rental unit doesn't have the required permit displayed, and reports it.

Not mentioned in the mailer is an ordinance passed last month that requires, in addition to registration forms, signed forms from tenants confirming that they know the city's trash collection rules. Mr. Ravenstahl signed the ordinance, which some landlords find particularly intrusive.

The city also has put together a software system that tracks "disruptive" events at homes -- both rentals and owner-occupied houses -- and will allow it to bill the owners of problem properties for public safety services.

That tracking system was the missing piece of an ordinance passed last year that compels the city to monitor everything from uncut grass citations to drug dealing to loose animal complaints. When three such problems occur at a property within two months, the city can demand a correction plan and send invoices for future police, fire and building inspection visits over the following six months.

"We commend the mayor on that one," said Mr. Mete. "We think that this is going to force the law enforcement end of this to provide to the landlord the means by which they can get someone evicted" when they are a problem in the neighborhood.

The disruptive property crackdown and rental registration were supposed to be in place months ago but were delayed due to technical and staffing problems.