The growth in jobs has slowed since the start of the year, with the retail sector showing the biggest decline, a study shows.
Recruiters Reed said there had been a 31% reduction in retail jobs, while those in energy and estate agents were down by a fifth.
Jobs in training, health, leisure and tourism were also down, it was reported, ahead of the latest official unemployment figures from the Office for National Statistics.
James Reed, chairman of Reed Recruitment, said: "The jobs market has slowed dramatically since the beginning of the year. It's possible that seasonality has led to a disjointed period for UK businesses.
"As Easter fell earlier in 2018, it's likely that holidays will have impacted growth, reflected in a marginal reduction in the number of new jobs being advertised at the end of the quarter.
"We've witnessed declines in key sectors such as retail, energy and estate agency. This is a clear warning sign that tougher times may lie ahead for the jobs market."
Meanwhile, a separate report warned that employers were finding it harder to recruit suitably skilled workers.