Three is the magic number, and Lawrence city commissioners are poised to get more serious about making local landlords and tenants understand it.

City commissioners at their Tuesday evening meeting will consider a host of rental regulations to crack down on landlords and renters who disobey the city ordinance that prohibits more than three unrelated people from living in a single-family home.

The proposal would require out-of-town landlords to hire a “resident agent” who serves as a city contact for enforcement matters. It also would beef up the city’s rental registration program, in effect making it a system where the city could deny problem landlords from leasing particular properties.

“These seem like excellent ideas to me,” said City Commissioner Bob Schumm. “These landlords understand what they’re doing when they overload these houses. Single-family neighborhoods are set up for a reason. Lots of people have their entire net worth in their homes, and they deserve better protection than what they’re getting today.”

Several neighborhood groups have complained that the city has been lax in enforcing the approximately decade-old ordinance that prohibits more than three unrelated people from leasing a single-family home. The result, many neighbors say, is that single-family neighborhoods have become prone to noise, litter, parking problems and other issues related to overcrowding of properties.

But on Monday, several landlords said the city had done a poor job of informing landlords of the possible rental changes, and some questioned whether the city was unfairly singling out only a portion of the Lawrence rental market for regulations. Only rental units in single-family neighborhoods are subject to the rental registration program. Apartment complexes and units in multi-family zoned areas — like the Oread neighborhood — aren’t subject to the rental registration program.

“It just targets a very small group of people, and it seems like they are trying to drive some of them out of business,” said Sofiana Olivera, of Lawrence-based A&S Rental Solutions. “To me it is really targeting the smaller owners.”

Among the regulations up for approval are:

• Absentee owners of rental property — defined as any owner who lives more than 40 miles outside the city — must hire a local, resident agent to be responsible for the property. The city will require contact information for the resident agent — including a cell phone number — so that the agent can be contacted if problems arise at the property.

• A rental license can be revoked if a property is considered to be a “public nuisance.” A property can be declared a public nuisance, if a property violates one or more of the following codes: anti-litter ordinance; disorderly house nuisance ordinance; property maintenance code; environmental code; or the land development code. Rather than revocation, the city also will have the option of placing a property on probation, which would give the property owner a set period of time to correct the violations.

• The city also will have greater authority to deny a property owner a rental license. If a property owner has had a rental license revoked for any property in the city during the last two years, that owner would be denied rental licenses on other properties in the community. The city also has a clause in the new regulations that allows it to deny an application for a particular piece of property, if that property has had its license revoked in the last two years.

• In addition to possible revocation of a license, a monetary fine can be levied against property owners who violate the code, and that includes landlords who allow more than three unrelated people to live in a single-family home. The new regulations increase the minimum fine from its current level of $250 to $500. The new code also makes it clear that the city’s Municipal Court judge has no ability to lower that fine.

• Tenants could get hit with a fine as well. If the tenants knowingly are violating the law by allowing more than three unrelated people to live in a single-family home, they could be subject to the fine. Previously, the city took the position that it was the landlord’s sole responsibility to ensure the code was followed.

City commissioners meet at 6:35 p.m. on Tuesday at City Hall.