The AFL-CIO and the Chamber of Commerce made a big show of solidarity last month, claiming they had "found common ground" on immigration and had come up with "principles [that] should guide legislation." Many news outlets reported this as a "breakthrough" on the path to comprehensive reform. We were skeptical at the time, noting that the "principles" were merely a series of vague platitudes that didn't spell out particulars of a bill. Conspicuously absent was a clear agreement on the main issue separating Big Labor and Big Business: a guest-worker program.

Our skepticism was vindicated when AFL-CIO President Richard Trumka conceded to ABC earlier this month that they hadn't yet reached a deal with the Chamber.

Neither the Chamber nor the unions have any problem with legalizing illegal immigrants. The devil is in the details. What Big Business wants out of the deal is the cheap labor that a guest-worker program would provide -- something Big Labor cannot abide. Unions argue there's no labor shortage, and that these programs hold down wages for native workers. There's also the problem that it is very hard to organize and collect dues from temporary workers.

Reports last Friday indicated that talks between Big Labor and Big Business were at an impasse. Why does all this matter? Because this same issue helped torpedo Congress's last attempt at comprehensive reform back in 2007.

At that time, Sens. Ted Kennedy and John McCain led a fragile coalition of reformers. Then-Sen. Byron Dorgan of North Dakota, a Democratic critic of immigration, sponsored an amendment backed by organized labor to strip their bill of its guest-worker program. Among those who voted for this AFL-CIO-backed "poison pill" was a freshman senator named Barack Obama. Without the guest workers, the Chamber backed out, and in doing so deprived the bill of crucial GOP support.

The Chamber and top labor leaders have been holding private talks this time around in the hopes of preventing another such debacle. Hence the PR effort last month to make it look like they were making progress. But history may well repeat itself. Although the GOP and the Democrats seem to have reached a tentative deal on legalizing existing immigrants, Big Labor is reportedly demanding a series of conditions to the guest-worker program. These include: setting the workers' wages above the prevailing wage; preventing the program from applying to most construction jobs; and creating a trigger that would let it apply only when unemployment falls below a certain level. Any of these provisions would defeat the purpose of a guest-worker program, as far as Big Business is concerned.

Both sides are now leaking the details of the negotiations and spinning them furiously in the hopes of pre-emptively dodging blame for failure -- a sure sign that talks are breaking down. Still, there is a lot of pressure on both sides to reach a compromise. Something may yet be hashed out.

But one thing is clear: If the talks do collapse and no comprehensive reform emerges, it will not be because lawmakers couldn't reach a deal on border security or the status of those "living in the shadows," as reformers like to say. It will be because those in Washington with economic interests related to the flow of immigration decided they weren't getting enough out of the deal.