The Trump administration issued a stern warning to U.S. companies as they began applying for coveted skilled-worker visas Monday, cautioning that it would investigate and prosecute employers that overlook qualified American workers for the jobs. The message came on the opening day of applications for American employers seeking visas known as H-1B, which are used mostly by technology companies to bring in programmers and other specialized workers from other countries.

"U.S. workers should not be placed in a disfavored status, and the department is wholeheartedly committed to investigating and vigorously prosecuting these claims," Tom Wheeler, acting head of the Justice Department's Civil Rights Division, said in a statement.

The Obama administration sued companies for violating the Immigration and Nationality Act's anti-discrimination provisions, including businesses that favored foreigners over U.S. workers. But Monday's warning in a news release at the start of the visa process appeared to be a first-of-its kind signal to employers not to put American workers at a disadvantage.