Economic growth slowed in Europe in the second quarter, but a range of other issues also discouraged firms from hiring permanent staff, said Adecco.
"Between the elections in Italy, Brexit, uncertainty in Catalonia, the strikes in France, there are lots of elements that weren't favourable to growth," said the firm's chief executive Alain Dehaze.
"Even if just barely, this lack of clarity had a tendency to push companies to prefer flexible hiring," he said after the company announced its second quarter results.
Overall, Adecco's revenue edged 1 percent higher to 6.1 billion euros ($7.0 billion) in April through June. Net profits fell by 11 percent to 170 million euros as the company stepped up investments to modernise and restructure its operations.
Revenue growth was fastest in Italy, at 11 percent when adjusted for factors like changes in the value of the currencies and the number of working days.
Italy has been gripped by uncertainty that was aggravated by an election that finally led to a populist government that has already moved to tighten restrictions on firing staff.
In France, Adecco's largest market, revenues rose by 8 percent for placement of temporary workers, with increases driven by the manufacturing, logistics, and automotive sectors.
France also has labour market rules that make it more difficult to reduce staff numbers when business slows, which employers say discourage them from taking on permanent employees.
"The impact of the strikes was clearly marked, but it is difficult to quantify in terms of hiring," said Dehaze.
Meanwhile in Britain and Ireland, Adecco also saw strong revenue growth of 6 percent thanks in part to winning new contracts. Ireland will feel the largest impact from Britain leaving the EU if London is not able to work out easy access to the single market.
In Spain and Portugal, revenues rose by 5 percent, after having grown strongly in previous quarters due to the recovery of the Spanish economy and uncertainty triggered by Catalonia's independence drive.
In the United States, where employers are having increased difficulty in finding workers, revenues rose 3 percent, although this represented the best result in three years. Adecco's shares fell by 2.6 percent in midday trading while the Swiss SMI
index was 0.3 percent lower.