FRAMED BY a brilliant blue sky, Joshua was on the roof, driving nails in a home rising at the Villages at Buckingham in Bucks County when a black Mercury Grand Marquis pulled up.

Four men got out and one hailed Joshua in the Portuguese of his Brazilian homeland.

The men were not from Immigration and Customs Enforcement. ICE never shows up at local work sites, say the guys I'm riding with, from Philadelphia's carpenters' union, Local 1073, which covers residential construction.

To check that out, I call and ask about the number of job-site arrests made around here. ICE spokesman Richard Roacha says arrests are not broken down by region or by industry. Enforcement is "centered on employers," he adds. That's good, but not having local or industry numbers is bad. Inexplicable, really.

Three or four times a week, Local 1073 guys visit construction sites to gather information, educate workers and cajole nonunion, but legal, workers into joining the union to get better pay, benefits and protection.

Union business agent Mark Durkalec, 47, is driving the Grand Marquis, with me riding shotgun. In the back seat are union representative Bill Dykan, 47, and carpenter Anilson Borgas, 46, who translates when necessary.

A Brazilian who became an American citizen in 2003 - it took almost five years and $3,000 in lawyers' fees - Borgas takes the unregulated arrival and employment of his former countrymen personally. It is an attack on his livelihood, his family, his rights as an American citizen.

In Buckingham, when Borgas asks Joshua whom he works for, Joshua squints and looks at the sky.

He doesn't know.

Another man on the site says two of the men pay taxes, the four others don't.

Joshua's confusion is understandable, since he works for a subcontractor and is likely falsely classified as an independent contractor. That means he gets no protection due employees and probably pays no taxes.

"We say illegal workers. It's really illegal employers," says Dykan, a guy with a priest's easy ability to talk with anyone.

On "Good Day, Philadelphia" a few weeks back, Councilwoman Maria Quinones-Sanchez spoke on behalf of illegal workers, parroting the tired cliche that they do only jobs Americans won't.

Quinones-Sanchez crossed a line when she added, "I do not foresee a union carpenter going out to work the fields."

Maybe union carpenters won't do field work, but they will do carpentry, and those jobs are being sucked up by the undocumented workers who accept lower pay than any American would - or should.

On the work sites we visit in what they call "the counties" ringing Philadelphia, we see lots of work done by undocumented workers hired by unscrupulous employers often paying them under the table and below decent rates. Illegal workers will accept as little as $7 an hour for working from sunup to sundown. That's a miserable $18,000 a year, but actually less because carpentry is seasonal work.

The issue isn't where they come from, but how their exploitation undermines the standard of living for Americans - and for legal immigrants who did the right thing and waited their turn to come here.

Nor is this just a "union" problem: Contractors who offer fair wages, pay taxes and play by the rules are victimized by lowballing criminal competitors.

About 15 years ago, Gary Wolfgang, of G.L. Wolfgang Construction, in Doylestown, noticed foreign crews coming in and "unreasonably low" bids on jobs.

"I went as low as I could go and I was barely able to pay taxes and insurance," Wolfgang says. "It was impossible for them to be legal."

After five years, he says, "I was driven out of the counties." He became a union contractor in Philadelphia, where "there was a more level playing field," he says.

Looking at downward spiraling wages, created in part by illegal workers, I wonder why anyone would support this attack on the American dream of a healthy life, a decent place to live, two weeks' vacation and an education for his kids.

Even if they don't mean to do it, illegal immigrants are killing that dream.

Politicians like Quinones- Sanchez must remember their first obligation is to the Americans who elected them.

E-mail stubyko@phillynews.com or call 215-854-5977. For recent columns: