Mexican immigrants register at a Citizenship Application Assistance Day event on March 23, 2013 in New York City. (John Moore/Getty Images)

A worsening dispute over a new guest-worker program has emerged as the most serious obstacle to a bipartisan deal on immigration, threatening to delay the unveiling of a Senate bill early next month.

The impasse has prompted a bitter round of name-calling between labor and business groups, which accuse each other of imperiling comprehensive immigration reform.

The Obama administration has remained on the sidelines as the standoff has worsened, calculating that the president would risk alienating Republican senators crucial to the process. Obama said this week that the issue is “resolvable.”

The guest-worker issue helped derail the last serious attempt at reform in 2007 with assistance from Obama, then a U.S. senator from Illinois. The current attempt at reform is being led by a bipartisan group of eight senators, who are attempting to fashion model legislation for a broad immigration overhaul.

The dispute centers on rules governing the “future flow” of migrants who come to the United States for menial jobs. Republicans, citing business interests, want to give temporary work visas to up to 400,000 foreign workers a year at low wages. But unions and many Democrats, fearing the effect on U.S. workers, want fewer workers and higher pay under the program.

Senators involved insist that they remain on schedule to complete a bill, including a path to citizenship for 11 million illegal immigrants, in early April. Obama also expressed confidence this week that the guest-worker disagreement could be solved.

“I don’t agree that it’s threatening to doom the legislation,” Obama said in an interview Wednesday with Telemundo, the Spanish-language TV network. “Labor and businesses may not always agree exactly on how to do this, but this is a resolvable issue.”

But behind the scenes, negotiations over the guest-worker program — and the White House’s refusal to take a position — have soured relations between the AFL-CIO and the U.S. Chamber of Commerce, which a month ago joined hands to publicly proclaim agreement on an overall plan.

“Unions say they want a guest-worker program, but their behavior is to the contrary,” said Geoff Burr, the Associated Builders and Contractors’ vice president for federal affairs. “They are insisting on a program that no employer would consider using.”

Union officials think that they have leverage because they have publicly committed to supporting Obama’s push for a path to citizenship — a key issue for Hispanic voters, who overwhelmingly supported the president’s reelection last year.

“This is not what Barack Obama campaigned on,” AFL-CIO spokesman Jeff Hauser said. “I don’t understand why people believe business has a seat at the main table after fighting for anti-citizenship candidates in 2012.”

As a senator eyeing union support for a White House bid, Obama voted in favor of an amendment to an immigration bill in 2007 that would have eliminated a new guest-worker program after five years. The amendment, which passed by one vote, has since been cited as a key reason that immigration legislation failed to advance that year.

Obama made no mention of a guest-worker program in a set of immigration principles that he laid out in a January speech in Las Vegas. The omission was notable, considering the bipartisan Senate group had included the idea in its principles that same week.

Instead, the White House has deferred to the Senate group, which includes four Democrats and four Republicans, to work out an agreement.

“If it’s included in line with the other principles that the president has rolled out in terms of what should be included in comprehensive immigration reform, that’s certainly something that we could support,” White House spokesman Josh Earnest said Wednesday of a guest-worker program. “But we’re going to reserve judgment on what that looks like until it’s actually produced.”

Administration officials say privately that the Senate group asked the White House to give the lawmakers “space” to take the lead in finding common ground between labor and business. Obama also is mindful of causing a political firestorm if he is seen trying to upstage the efforts of the senators, officials said.

But Obama has met separately over the past two months with business and labor leaders at the White House and has vowed to step in with his own legislative proposals if the Senate is unable to come to an agreement. The White House announced this week that the president will travel to Mexico and Costa Rica in early May to highlight cultural and economic ties.

One Republican Senate aide involved in the talks said the White House’s absence from negotiations has helped ensure that the process does not become “overly politicized.”

But, the GOP aide added: “Everyone understands this is a critical piece for future flow. . . . Eventually, the White House will have to make a choice.”

The senators maintain that the negotiations continue to move forward. Four members of the working group inspected border-control measures in Arizona on Wednesday, and Sen. Charles E. Schumer (D-N.Y.) said afterward that the group’s work on the legislation is “90 percent” complete.

The guest-worker program is not the only contentious area. The bill is likely to include a large increase in visas for high-tech workers and the elimination of some categories of family visas, two areas that have provoked strong opposition from advocates who fear it could make it harder for families to be reunited.

The guest-worker dispute broke into view last week when U.S. Chamber of Commerce officials went public with their concerns over the process, leading to angry responses from AFL-CIO officials.

The Chamber has called for 400,000 visas for guest workers, along with the ability for those workers to switch jobs once they are in the United States. Union officials countered with an offer of 10,000 visas and said that foreign workers should be allowed to pursue citizenship once they have entered the country.

The senators have reportedly agreed to cap the program at 200,000 visas per year, starting at a much lower figure and moving up as the economy improves.

But the biggest sticking point has been wages. The chamber wants to pay the foreign workers based on a government calculation of the prevailing wages of American workers — based on the minimum wage and on regional and industry norms. Unions are holding out for a higher pay scale based on median wages for each industry.

Business leaders contend that the AFL-CIO — and, by association, the White House — are not negotiating in good faith.

“The president is obviously close to unions on this issue. The constituencies they’re trying to keep happy with immigration reform do not care about this piece of it,” said Tamar Jacoby, president of ImmigrationWorks USA, a federation of small-business owners that supports immigration reform.

Jacoby said that based on last year’s election results, the White House is calculating that “Republicans so badly need to get on the right side of history with Latino voters, they will throw business to the wolves and throw future immigrants under the bus.”

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