Employers seeking visas for highly skilled workers will need to provide additional details in their petitions if the employment involves working at a third-party worksite, as part of what the Trump administration says is an effort to root out fraud and abuse.

The U.S. Citizenship and Immigration Services policy memorandum—which took effect Feb. 22—says that for an H-1B visa petition involving a third-party worksite to be approved, the petitioner must show “by a preponderance of evidence” that, among other...