Increased vigilance in Fairfax County over housing-code violations is stirring uneasy tension in some neighborhoods where residents — often recently arrived immigrants — are crowding into single-family houses or running unlicensed businesses from their back yards.

Annoyed neighbors increasingly are utilizing a county system that allows them to e-mail or phone in complaints about various concerns, such as parked cars crowding driveways and side streets or unkempt yards loaded with work materials.

The callers, who generally are not recent immigrants, say they are concerned with quality of life, not race or ethnicity. But homeowners who have been visited multiple times by county inspectors, especially those who have not been cited for serious violations, say they feel targeted.

“It feels like we’re being harassed,” said Jimmy Chung, who is among a group of Vietnamese immigrants using a house as a site for Buddhist meditation. Inspectors, he said, have “come down to the temple a thousand times already. We’ve been doing exactly what they tell us to do.”

The frustration on both sides is palpable and in some ways stems from an earlier problem in Fairfax: the proliferation of illegal boarding houses in several neighborhoods that had growing Asian, Latin American and Middle Eastern populations.

In 2009, local and federal officials busted a $24 million mortgage fraud scheme anchored in those neighborhoods. The scheme involved straw buyers purchasing dozens of houses — many of them newly built “McMansions” — that were turned into multifamily residences. The homes became nuisances because of parking and other problems and eventually went into foreclosure.

County officials said community alarm from that case, along with the overall problem of crowding, led to an overhaul of zoning enforcement in the county and the creation of a reporting system that depends on resident complaints.

About 20,000 phone calls per year come in now, leading to as many as 9,000 investigations into allegations of crowding, unkempt lawns, illegal businesses and other problems not related to houses, officials said. About two-thirds of the complaints end with a finding of a code violation. Most violations are quickly fixed.

“We respond to residents’ complaints,” said Jeff Blackford, director of the zoning compliance department. “They have the best pulse on the neighborhood. We want them to notify us so we can respond to that.”

But the increased community watchfulness — combined with a changing cultural landscape in Fairfax and what are sometimes innocent mistakes made by homeowners new to the country — has been a double-edged sword, officials say.

On one hand, neighbors are more aware of homes on their block that have as many as six or seven cars parked in the driveway. In 814 cases last year, houses were indeed places that had been illegally converted into apartments or were otherwise too crowded, county records show.

In many other cases, however, the driveways were crowded simply because the homes were owned and occupied by large immigrant families, some of whom built legal additions to make room for siblings or parents.

Distinguishing between the two situations can be tricky, and there are risks violating a homeowner’s constitutional rights against illegal search and seizure, officials say.

“There is a delicate balance at play between authority of government and privacy rights,” said Supervisor Penelope A. Gross (D-Mason), whose district generates among the highest number of code violation complaints in the county.

“Some people want us to show up at midnight and count how many people are sleeping in beds,” Gross said. “We don’t do that, and we shouldn’t do that. That’s not how we enforce the law.”

Residents who complain to the county often do so anonymously, saying they fear retribution or charges of bigotry if their names are attached to their calls. Fairfax officials say that makes it harder to follow up.

“People don’t want to be viewed as racist,” said Mollie Loeffler, who as chair of the Mason District Council of civic associations has spearheaded a campaign to push county inspectors to pursue violations more aggressively.

That awkwardness “adds to the anger,” Loeffler said. “And there’s a lot of anger going on.”

During a recent afternoon, Loeffler and some other homeowners in the Annandale area piled into a van to point out houses that they consider repeat code violators. One is nicknamed “the Blight House.” Others are “the Apartment” and “the Car Lot.” All had several cars parked in the driveway, junk in the yard or signs of commercial activity in the back.

“This is the car repair place,” Jon Clark said as the van pulled up to a brick house with a corrugated metal car port in its sprawling back yard.

According to Fairfax County court records, a tow truck service and junk yard operated at that address until it was shut down in 2012.

Clark, who lives down the street, said he believes an unlicensed car repair business is still operating at the residence. A complaint about dilapidated structures on the property is under investigation.

Patricio Paucar, 38, lives with his family inside the house known as “the Apartment,” a majestic-looking home with eight bedrooms, six bathrooms and several cars parked diagonally in a long driveway.

Paucar said his wife, some siblings and their collective children live with him in the home — 14 people in all. Many have their own cars. Reacting to neighbors’ complaints, county inspectors have investigated the house seven times since 2009, citing them once for multiple occupancy but after that declining to act.

“It’s kind of annoying,” said Paucar, a professional house painter whose family immigrated to the United States from Colombia and Ecuador. “We’ve been living here 15 years.”

At the same time, Paucar said, he has seen instances of crowding elsewhere in the county and — sort of — understands the concerns about his home.

“I went to do a painting job and there were 30 people in the house,” Paucar said. “None of them looked alike.”

Mohammed J. Abdlazez was less charitable about the eight inspections conducted at his house since 2009. County officials were called about the used-car business that Abdlazez, an immigrant from Jordan, conducts from his front yard. He openly admits the business is unlicensed, but he does not understand what the fuss is about.

“We are nine people inside this house. I have to feed my children,” Abdlazez said. “Why are they picking on me? Because of my name.”

Abdlazez jumped behind the wheel of a BMW sport-utility vehicle he is trying to sell and offered a visitor his own tour of the neighborhood, in the Alexandria section of Fairfax. He pointed out house after house with several cars parked in the driveway.

“Look at this one with five cars — one, two, three, four, five,” he said, voice rising. “If you’re going to give me a ticket, why not give that guy a ticket? Give everybody a ticket, not just me!”