The number of job vacancies advertised online fell in August, the fifth drop in the past six months.
The Monster Employment Index UK dipped seven points to 167 last month, down from 174 in July and 192 in February. Only January posted lower results this year.
"Previously job seekers had the upper hand in the labour market, but the balance is now shifting," said Hugo Sellert, head of economic research, Monster Worldwide.
"The recent decline in the index shows jobs are now getting harder to come by as businesses across the UK ease back on their hiring in response to the slowing economy."
"Not all sectors are feeling the pinch, though. Advertised vacancies in the healthcare and social work sector continue to rise, indicating mounting demand for nursing and medical care professionals."
A seasonal dip in training and education sectors of 45 points was expected, experts said. The index also saw a sharp drop in online hiring for the hospitality and tourism industries that is expected to be corrected in the lead-up to Christmas.
Available jobs in building and manufacturing sectors also dropped by nearly one third.