The work stoppage from 3:00-5:00pm forced the UN's top rights body to delay a panel, featuring its rights chief and the president of the General Assembly, for an hour.
After Secretary-General Antonio Guterres addressed the Conference on Disarmament, striking translators left the room and the remaining dignitaries opted to speak exclusively in English rather than postpone the meeting.
It was unclear how many of around 9,500 UN staff members in Geneva actually halted work, but what looked like several hundred people gathered at the start of the stoppage near the UN Human Rights Council to voice their displeasure with wage cuts that took effect last week.
UN Geneva staff received their first pay slips showing a 3.5-percent salary cut, with the knowledge the cut will swell to five percent by June, according to Ian Richards, who heads the UN staff unions association in Geneva.
The work stoppage had initially been announced for Tuesday, but Richards told AFP it had been advanced by a day after the UN indicated it was looking at "contingency plans" to keep operations moving forward.
He said a large demonstration was also expected to take place on Tuesday.
Rights council spokesman Rolando Gomez said the delay in the body's programme on the opening day of its main annual session may not have been long, but it was felt.
"Every minute counts in the council amidst a very, very jammed schedule," he told AFP, adding that Monday's session would go into overtime, entailing additional cost to keep translators and others past their usual cut-off time.
Monday's demonstrators held up placards voicing "No confidence in ICSC", or the International Civil Service Commission (ICSC) – a body appointed by the UN General Assembly to govern UN employees which has ordered deep cuts to pay and benefits for many staff around the globe.
"What is happening is just ridiculous," one of the striking workers told AFP, requesting anonymity.
"Statisticians from all the organisations have shown that their calculation methods (for the wage cuts) don't add up, but they won't listen," he told AFP.
A letter sent by the unions to UN chiefs last week charged there had been a "substantial deterioration in the employment conditions of UN staff around the world, caused by ICSC's findings, recommendations and decisions."
UN employees are considered among the highest paid civil servants in the world, but the ICSC-mandated cuts will be painful in pricy Geneva, the unions say.
Staff stationed in a number of other countries will take an even heavier blow.
According to the unions, the most recent ICSC decisions include 10-percent cuts in Bangkok and 25 percent in Tokyo.