The company sponsored public forums to promote the idea and donated $100,000 to a group unsuccessfully fighting Proposition 200 in Arizona, which requires proof of citizenship from people seeking to vote or collect certain public benefits.

As the debate moved to Washington, Western Union gave money to many groups supporting legalization plans. The U.S. Chamber of Commerce received nearly $1 million, a Chamber official said, while an Illinois group used some Western Union money to bring busloads of immigrants to Capitol Hill. When a bipartisan Senate bill emerged last spring, Western Union officials flew to Washington to lobby directly, urging Sen. Ken Salazar, D-Colo., to support the measure. He eventually did, though it ultimately failed.

"Most companies are afraid to speak up," said Frank Sharry, executive director of the National Immigration Forum, which has received $40,000 from Western Union over the past three years. "When it got hot, they stayed with it."

But proponents of stricter border controls see commerce, not courage, at play. "Western Union has decided that its business model depends on a continuing flow of illegal immigrants," said Mark Krikorian, director of the Center for Immigration Studies, which advocates low levels of immigration.

Western Union's latest battle is with the Arizona attorney general, Terry Goddard, who in 2004 began seizing money transfers into Arizona that he suspected were mean to pay human smugglers. The effort led to hundreds of arrests but also froze legitimate transfers and scared away customers, costing Western Union millions.

After two years of cooperation, the company sued last year when Goddard, a Democrat, expanded his request to cover transfers from across the United States to Sonora, Mexico. In September, an Arizona court ruled for Western Union.

The company is "protecting an illegal enterprise in human smuggling," Goddard said. "It's outrageous."

The company spun off from First Data a year ago, and it has an estimated global market share of 14 percent, versus 3 percent for its closest competitor, MoneyGram. Though Western Union has responded to increased competition by cutting its charges, it typically remains the most expensive service.

An Oakland group, the Transnational Institute for Grassroots Research and Action, has begun a boycott campaign, demanding that Western Union lower its prices and increase its corporate giving. But it has gained little traction, in part because of the company's recent courtship of migrant groups.

One former critic who now gives Western Union grudging credit is Donald F. Terry, an official at the Inter-American Development Bank. He has spent years trying to get more migrants to use banks, so they could establish financial histories and qualify for loans.

But banks have failed to fully welcome migrants, he said, while Western Union and other money transfer companies have more locations, better hours and agents who know their customers' language and culture.

"You could say they were ripping people off, or you could also say they're providing a service that poor people desperately needed and were willing to pay for," Terry said. "Any consumer company in the world would like to have the customer loyalty they have. They're doing something right."