Although US workers’ pay and benefits steadily increased last year, it was at a slower rate than in 2018, the Labor Department has said in a new report.

The federal employment cost index found that total salaries and benefits such as health insurance increased 2.7% in 2019, down from 2.9% in 2018. For the last three months of 2019, workers’ compensation grew 0.7% – the same rate as the previous quarter.

According to the Labor Department, the slowdown in salary and benefit growth comes as a shock to economists – particularly when the current unemployment rate of 3.5% is at a half-century low, and it remained at that level for most of 2019.

The Associated Press reported that the employment cost index’s figures line up with data from a previous monthly jobs report, which showed that annual growth in hourly wages dropped from 3.4% in early 2019 to 2.9% in December.

It is speculated that the slowdown in hourly wage growth is a reflection of the surge in the number of lower-paid workers. Due to low levels of unemployment, more companies are hiring people who previously were not working or were looking for work, and mostly for lower-paying jobs.