The United Nations commemorated the 10th anniversary of the single deadliest assault in the organization’s history on Monday, the bombing of its Baghdad offices that killed 22 people, with Secretary General Ban Ki-moon warning in a speech that since then “the attackers who target us have grown more sophisticated, more brazen and better armed.”

But in some ways Mr. Ban’s commemoration remarks at the United Nations headquarters, on a day it has designated World Humanitarian Day, were overshadowed by aggrieved staff members, whose union representative presented Mr. Ban’s office with a letter asserting that his internal labor policies had compromised their safety and security.

They said they were particularly upset by what they called Mr. Ban’s refusal to bargain with their union over issues related to staff assignments in hardship posts and conflict zones.

The representative, Ian Richards, vice president of the Staff-Management Committee, a group of all 15 union chapters in the United Nations work force, announced that he was delivering the letter as part of his speech at the commemoration event, which followed Mr. Ban’s remarks. Mr. Richards also asserted that United Nations workers had become frequent targets.