Aug 27 (Reuters) - Top oilfield services firm Schlumberger NV (SLB.N) is asking U.S. employees to disclose their COVID-19 vaccine status and said more customers are mandating vaccinations as a condition for working on their job sites, the company said on Friday. Oil and gas companies have begun ordering certain employees and new hires get vaccinated as Delta variant infections and hospitalizations rise. The Food and Drug Administration this week gave full approval to the Pfizer BioNTech COVID-19 vaccine, making it easier for companies to require the shot. "Customers have begun to mandate vaccinated personnel as an eligibility requirement to service their operations," James R. McDonald, president of Schlumberger"s Americas Land business, said in an Aug. 27 email sent to employees and seen by Reuters. Several offshore operators have already enforced the mandate, he said. As an oilfield service provider, Schlumberger"s employees are often working on job sites operated and run by other oil and gas companies. "All employees and contractors will need to disclose their vaccination status through a protocol that protects this information under U.S. regulatory guidelines," the email also said. Schlumberger in a statement said employees have an option to decline to disclose if they wish. Oil producers Hess (HES.N) and Chevron (CVX.N) have said workers in their Gulf of Mexico operations would be required to be fully vaccinated by Nov. 1. Shale major Pioneer Natural Resources (PXD.N) also is requiring new employees to be fully vaccinated before their first day of work. read more Schlumberger"s call for employees to disclose their vaccination status, McDonald said the email, will allow the company to "enhance our mitigation measures to keep people safe and enable business continuity."