The number of Americans filing applications for new unemployment benefits climbed by more than expected last week.

Initial jobless claims rose by 10,000 to a seasonally adjusted 231,000 in the week ended December 29, the Labor Department said Thursday.

Economists had expected 220,000 new claims. The prior week’s claims were revised up by 5,000 to 221,000.

Despite the higher than expected numbers and the upward revision, jobless claims numbers remain at levels consistent with a tight labor market and the lowest levels since the 1960s.

Weekly jobless claims can be volatile, particularly around seasonal changes and holidays. The four-week moving average of claims, which smooths out some of the week-to-week jumpiness, fell by 400 to 218,750.

Jobless claims have been closely watched this year because they are a proxy for layoffs. Despite many claims that trade disputes have weighed on American businesses, the very low levels of jobless claims indicate that U.S. tariffs and retaliation have not come at a cost to American jobs. To the contrary, the job market has outperformed the expectations of most economists and remains a bulwark of the economy.

Businesses may be reluctant to lay off workers because they view the current U.S. economy as one in which hiring is difficult. The unemployment rate held at 3.7 percent in November, matching the lowest rate in nearly 50 years.

The government will report the number of nonfarm jobs added to the economy on Friday. Payrolls are expected to rise by 177,000 jobs last month after rising 155,000 in November.