The U.S. Chamber of Commerce and AFL-CIO reached a tentative agreement to support increasing lawful migration through a guest-worker program for lower-skilled migrants. The details are obscure, but this agreement is an essential first step for successful immigration reform — a step so far ignored by the Obama administration.

Without a guest-worker program, quite simply, immigration reform will fail.

Overwhelmingly, immigrants come to the United States because they want jobs, and American businesses have jobs to give. Legalizing the unauthorized migrants already here is a sound policy, but without a legal channel for workers to come, others will continue to enter the country illegally.

Policymakers seem to forget that there is recent evidence to this effect. Ronald Reagan instituted an amnesty in 1986, but unauthorized immigration continued unabated. Increased border and immigration enforcement — and it did increase — couldn’t stem the tide.

It is foolish to expect legalization and enforcement alone to stop unauthorized immigration. The demand is too strong on both sides of the labor equation. We need reforms that adapt to that reality.

Why is President Obama ignoring a guest-worker visa program? Because unions — one of the president’s most valued constituencies — have historically opposed guest workers.

A 2007 immigration reform effort largely failed because of union efforts to kill it. Late in the game, Senate Democrats amended the bill to end its guest-worker program after five years. The amendment passed 49–48 — with then-Sen. Obama, ominously, voting in favor. As a result, Republicans and business interests that supported increased lawful immigration withdrew their support, and the reform effort collapsed.

At the time, the leaders of the AFL-CIO, the Teamsters, and other unions all wrote letters opposing the guest-worker program. James P. Hoffa of the Teamsters opposed a guest-worker program because it would “[force] workers to toil in a truly temporary status with a high risk of exploitation and abuse by those seeking cheap labor.”

But the employer abuse issue is a straw man. There is a rather simple remedy: visa portability, which would allow guest workers to easily switch jobs. The ability to quit a job without the legal risk of deportation would give guest workers the ability to effectively enforce their own labor standards: They could depart an abusive employer without fear of deportation.

Instead of more migrant freedom, labor leaders are supporting more regulations for guest-worker visas. The Obama-endorsed blueprint wants reform to “protect workers by ensuring labor protections.” But those so-called protections have already made current lower-skilled guest-worker visas too costly for American employers — a by-product unions favor.

To their credit, unions support legalization of current unauthorized immigrants and family reunification. But from the Chinese Exclusion Act in 1882 through the race-based quotas of the 1920s to today, unions have supported every migrant-worker restriction.

César Chávez’s United Farm Workers (UFW) lobbied hard to end the Bracero Program, a 1940s guest-worker program created to address an agricultural labor shortage created by World War II. UFW members beat up unauthorized migrants, formed a “wet line” (their words) on the border to stop migrants, and reported unauthorized immigrants to the Immigration and Naturalization Service.

If there is a model for a successful guest-worker program, however, the Bracero Program is it. Under Bracero, immigrants could work temporarily, but they had to leave the United States every season. American farms got the labor they demanded, immigrant workers made money, and agricultural production increased.

The program was so successful that it was extended until 1964. It combined enforcement that funneled migrants into a legal system with an unlimited temporary migration system. Often, Border Patrol agents enrolled unauthorized immigrants they arrested in the Bracero Program and let them return to work — this time lawfully.

Mexican workers thinking of entering the United States illegally overwhelmingly chose the legal Bracero option instead. Throughout the 1950s, unauthorized immigration declined by 95 percent. If a Bracero-type guest-worker visa existed today, one that allowed migrants to switch jobs and work in nonagricultural areas, unauthorized immigration would dramatically decrease.

However, this solution remains off the books because of the prior opposition of labor unions.

Today, the AFL-CIO has agreed in principle to a guest-worker visa program — but the gap between principle and legislation is wide. If history is a guide, unions and their allies, although they are playing nice now, will oppose guest-worker visas when the details are released. But successful reform will require ignoring union pressure and allowing more worker migration.