ORLANDO, Fla.  The employees who kept the data systems humming in the vast 
Walt Disney fantasy fief did not suspect trouble when they were suddenly summoned to meetings with their boss.
While  families rode the Seven Dwarfs Mine Train and searched for Nemo on  clamobiles in the theme parks, these workers monitored computers in  industrial buildings nearby, making sure millions of 
Walt Disney World  ticket sales, store purchases and hotel reservations went through  without a hitch. Some were performing so well that they thought they had  been called in for bonuses.
Instead, about 250 
Disney employees 
were told in late October  that they would be laid off. Many of their jobs were transferred to  immigrants on temporary visas for highly skilled technical workers, who  were brought in by an outsourcing firm based in India. Over the next  three months, some Disney employees were required to train their  replacements to do the jobs they had lost.
I  just couldnt believe they could fly people in to sit at our desks and  take over our jobs exactly, said one former worker, an American in his  40s who remains unemployed since his 
last day at Disney on Jan. 30. It was so humiliating to train somebody else to take over your job. I still cant grasp it.
Disney  executives said that the layoffs were part of a reorganization, and  that the company opened more positions than it eliminated.
But  the layoffs at Disney and at other companies, including the Southern  California Edison power utility, are raising new questions about how  businesses and outsourcing companies are using the temporary visas,  known as H-1B, to place immigrants in technology jobs in the United  States. These visas are at the center of a fierce debate in Congress  over whether they complement American workers or displace them.
According  to federal guidelines, the visas are intended for foreigners with  advanced science or computer skills to fill discrete positions when  American workers with those skills cannot be found. Their use, the  guidelines say, should not adversely affect the wages and working  conditions of Americans. Because of legal loopholes, however, in  practice, companies do not have to recruit American workers first or  guarantee that Americans will not be displaced.
Too  often, critics say, the visas are being used to bring in immigrants to  do the work of Americans for less money, with laid-off American workers  having to train their replacements.
The  program has created a highly lucrative business model of bringing in  cheaper H-1B workers to substitute for Americans, said Ronil Hira, a  professor of public policy at Howard University who studies visa  programs and has 
testified before Congress about H-1B visas.
A  limited number of the visas, 85,000, are granted each year, and they  are in high demand. Technology giants like Microsoft, Facebook and  Google repeatedly press for increases in the annual quotas, saying there  are not enough Americans with the skills they need.
Many  American companies use H-1B visas to bring in small numbers of  foreigners for openings demanding specialized skills, according to  official reports. But for years, most top recipients of the visas have  been outsourcing or consulting firms based in India, or their American  subsidiaries, which import workers for large contracts to take over  entire in-house technology units  and to cut costs. The immigrants are  employees of the outsourcing companies.
In  2013, those firms  including Infosys, Tata Consultancy Services and  HCL America, the company hired by Disney  were six of the top 10  companies granted H-1Bs, with each one receiving more than 1,000 visas.
H-1B  immigrants work for less than American tech workers, Professor Hira  said at a hearing in March of the Senate Judiciary Committee, because of  weaknesses in wage regulations. The savings have been 25 percent to 49  percent in recent cases, he told lawmakers.
In  a letter in April to top federal authorities in charge of immigration, a  bipartisan group of senators called for an investigation of recent  H-1B-driven layoffs, saying, Their frequency seems to have increased  dramatically in the past year alone.