As technology gets better and cheaper, there are lots of new tasks it could take over. “It is a new, uncharted area for our company and our industry as a whole,” Mr. Atkinson said. “We have talked about one or two brands being fully automated and self-service for the guest.”

David Autor, an economist at M.I.T., says it is plausible to foresee a future in which — as airlines have done — hotels deploy humans to tend to elite guests and automated systems for everybody else. Workers generate costs well beyond their hourly wage, Professor Autor argued. They get sick and take vacations and require managers. “People are messy,” he noted. “Machines are straightforward.”

Last year, the McKinsey Global Institute issued a report projecting that technology would drive a 30 percent decline in jobs in food service and lodging from 2016 to 2030. That’s almost on a par with the 38 percent decline in manufacturing jobs from 1960 to 2012.

Unions would rather not have manufacturing’s story repeat itself in the service sector. “We are trying to get ahead of that,” said Anand Singh, president of Unite Here’s local in San Francisco. “We are not Luddites, but we are seeking a real voice at table.”

The International Brotherhood of Teamsters is also worried about technologies hurtling into the present. As it squared off for contract negotiations with United Parcel Service this year, the union put a bold proposition on the table: to prohibit using drones or autonomous vehicles to deliver packages. But in September, when the union sent the agreement to members for a ratification vote, there was no such provision.