The jobs of the nation's citizen-soldiers are supposed to be safe while they are serving their country: Federal law does not allow employers to penalize service members because of their military duties.
Yet every year, thousands of National Guard and Reserve troops coming home from Afghanistan and elsewhere find they have been replaced, demoted, or denied benefits or seniority.
Government agencies are among the most frequent offenders, accounting for about a third of the more than 15,000 complaints filed with federal authorities since the end of September 2001, records show. Others named in the cases include some of the biggest names in American business, such as Wal-Mart and United Parcel Service.
With good jobs still scarce in many states, the illegal actions have contributed to historically high joblessness among returning National Guard and Reserve members - as high as 50 percent in some California units - and created a potential obstacle to serving.
"The whole point of the National Guard and reserves, how they save the country money, is they get paid only when they are serving," said Sam Wright, director of the Service Members Law Center at the Reserve Officers Association. "It's a great deal for the country, but if we don't protect their civilian jobs they aren't going to volunteer and serve."
Veterans' advocates say that the heavy use of the nation's citizen-soldiers to fight the wars in Iraq and Afghanistan placed a burden on employers in a tough economy. Even as 11 years of war wind down, Guard and Reserve members are being called up for peacekeeping and other duties around the world.
The Uniformed Services Employment and Reemployment Rights Act, a 1994 law that strengthened job protections for returning troops first introduced during World War II, requires that service members are re-employed in the type of position they would have attained if they had not been called to active duty.
Just how many service members are being denied jobs illegally is impossible to know. The nonpartisan Government Accountability Office estimated in 2005 that fewer than a third of service members with complaints seek help from the government. Many don't file lawsuits, either.
Even so, the Labor Department and Office of Special Counsel, which investigate complaints for possible prosecution, have seen cases surge from 848 in fiscal 2001 to 1,577 in the 12 months ending in September 2011. Last year, the agencies handled 1,436 new cases, according to preliminary figures.
A Defense Department program that tries to mediate disputes handled 2,884 cases in fiscal 2011 alone, including 299 that went to the Labor Department when they could not be resolved informally.
Although the law says the federal government should be a "model employer," federal agencies accounted for nearly 20 percent of the formal complaints in fiscal 2012, about twice the share recorded in 2007. The departments of Defense and Veterans Affairs lead the way with 105 and 47 complaints, respectively.
President Obama instructed federal agencies last July to intensify efforts to ensure compliance. But officials say it has been a challenge to ensure that supervisors working at offices across the country are familiar with the requirements.
Obtaining redress can take months, if not years. For service members, the experience can be a maddening double-blow.
Government agencies and Fortune 500 companies - especially military contractors - are major employers of people who serve in the armed forces and might be expected to experience the most disputes. State and local governments accounted for more than 20 percent of the complaints last year and private companies nearly 60 percent.
Government officials note that many of these cases are the result of misunderstandings that may not amount to breaking the law.
"It's not an intuitively obvious law," said Lt. Col. Melissa Phillips, deputy director of the Defense Department's Employer Support of the Guard and Reserve. "We have individual supervisors who are continually changing, and so it's a continual education process."
A Labor official, who was not authorized to speak on the record, said most disputes are resolved without recourse to the courts. He acknowledged past problems, but said the department has revamped its training for investigators. It now takes an average of 60 days to complete an investigation, he said.
But attorneys for aggrieved service members say some employers have grown sophisticated about trying to get around the law. Rather than wait to see whether deploying troops will want their old jobs back, some hand out pink slips as soon as they are notified that their employees are expecting orders. Others refuse to hire people who serve in the Guard and Reserve, a form of discrimination that is illegal but hard to prove.
The Labor Department investigated eight new claims against UPS last year and 11 in fiscal 2011. Verizon was the subject of six complaints in the last two years. Officials at the two companies declined to discuss cases but said they go out of their way to recruit and retain military members.
Wal-Mart was named in 29 cases, more than any other Fortune 500 company. Company officials did not respond to requests for comment.