U.S. oilfield supplier National Oilwell Varco Inc. is trimming its workforce, according to people familiar with the matter, as oil and gas customers have cut spending on services and equipment.

The company recently began offering voluntary early retirement to eligible employees, three people said. Any discussion of workforce cuts would be part of its second-quarter earnings call next week, said a spokesman for the Houston-based company, who declined to comment further.

Although global oil prices have rebounded from the market's 2014-16 downturn, profits at the service companies that provide drilling and well-completion services have not recovered to the same extent.

An index of oilfield service firms' operating margins fell to a negative 32.8 from negative 6.6 in the bank's earlier survey.

Halliburton Co., the largest provider of hydraulic fracturing services in the U.S., this week said it would cut 8% of its workforce in North America. The largest oilfield services provider by revenue, Schlumberger Ltd., this month said it expects softer demand for services in North America.

National Oilwell Varco provides equipment and other services to the oil industry. It had roughly 35,000 employees at the end of 2018, up from about 32,000 a year earlier, according to regulatory filings.

Its shares were up less than 1% at $22.01 on July 24.