A year after rallying for immigration reform, hundreds of thousands of undocumented workers and their supporters were back on the streets Tuesday protesting a steady rise in workplace raids and deportations.

Since last May's nationwide rally -- during which immigrant- and employee-rights  groups threatened work stoppages and business interruptions -- federal officials have deported more than 220,000 foreign nationals, according to U.S. Immigration and Customs Enforcement. In 2005, the federal government deported a total of 131,576 individuals, agency figures show.

According to some estimates, there are as many as 12 million undocumented immigrants living in the United States.

In April alone, federal agents arrested 148 undocumented immigrants over a four-day sting in Dallas, and 35 in a similar operation in Prescott, Ariz., the agency said. A week earlier, 23 workers were arrested at a concrete manufacturing plant in West Burlington, Iowa.

"ICE will continue to fulfill our congressional mandate to apprehend and deport those who entered our country illegally," Nuria Prendes, an agency field officer said following the arrests in Dallas, which so far has resulting in 84 deportation to Mexico.

Although none of the raids resulted in charges against employers, many are growing increasingly concerned about being held responsible for ensuring the legality of their employees.

Last month, President Bush called employer accountability a key element of immigration reform. In a speech to border patrol agents in Yuma, Ariz., he stressed the need for an improved verification system and tamper-proof identification cards for legal foreign workers.

Of the 60 million or so workers hired by U.S. employers every year, as many as 5 percent have undocumented status, Randel Johnson, the vice president of labor, immigration and employee benefits for the U.S. Chamber of Commerce, told a congressional committee last week.

Beyond legal troubles, he said, employers that hire undocumented workers are taking a big risk -- especially with federal raids on the rise.

"While the company might not suffer any legal action or fines, losing valuable members of the workforce and possibly closing down for even a short amount of time can often add up to significant financial losses, not including the less quantifiable harm such as negative publicity," Johnson said.

Congress is currently evaluating the benefits of an electronic employment-verification system as part of a broader overhaul of the immigration system.

In March, federal lawmakers also introduced a bipartisan bill requiring undocumented workers to return home before reapplying for permanent U.S. residency.  

In a survey of more than 4,000 small-business owners in October by Discover, only 19 percent said changes to immigration laws would impact their business.