The battle over bandwidth — that precious commodity that makes the high-tech world rock and roll — was rejoined this week with Transportation Secretary Anthony Foxx saying that cable companies should back off until there is proof that their ambition will not imperil automotive progress.

At stake is a sliver of bandwidth — 75 megahertz in the 5.9 GHz band — that has been reserved since 1999 for use in vehicle-to-vehicle communication, that era when on-board car computer systems will be able to communicate with one another and receive data from other outside sources.

But the bandwidth spectrum is finite, and as demand for it has mushroomed, so has the push to share some of that untrammeled bandwidth reserved for car talk. Foxx responded to the latest lobbying salvos in a conversation with reporters Tuesday.

“It’s my view that if we have something protected for a safety reason, until you have something definitive that gives you a basis to share it, then we should probably keep protecting it until we know for sure that we can have mixed uses without interfering with the fundamental purpose of it,” he said.

Foxx sent the White House a proposal in January that would require all new cars to be equipped with vehicle-to-vehicle communications. At the same time, Foxx reached an agreement with Commerce Secretary Penny Pritzker and Federal Communications Committee Chairman Tom Wheeler to test whether it would be safe for wireless devices to share the 5.9 GHz band.

Vehicle-to-vehicle communication is a concept forecast to one day prevent up to 80 percent of crashes that do not involve alcohol. Interaction between cars and infrastructure, such as signal lights, would allow a car computer to assess the risks ahead.

While the administration ponders what to do with Foxx’s proposal, the lobbyists have beaten a path to the White House.

Foxx’s comments came after groups that want a share of the 5.9 GHz pie, including the National Cable & Telecommunications Association, sent a letter to President Obama warning that connected-device use was soaring and “the spectrum resources that power our devices are perilously insufficient.”

“We must act now to find more unlicensed spectrum,” the groups wrote, asking the president to act swiftly.

Last week, the auto industry and safety groups fired back with a White House letter of their own.

“You received a letter from the cable industry and additional stakeholders suggesting that the transportation sector refuses to share the 5.9 GHz band used for connected vehicle technology with WiFi. Nothing could be further from the truth,” said the letter, signed by more than 55 companies and organizations.

Their letter said that they had been working with the WiFi industry to find a way to share the bandwidth while “maintaining the integrity” of potential vehicle-to-vehicle communication.

“These efforts include the testing of at least two potential sharing solutions that the Federal Communications Commission, the Department of Transportation, and the National Telecommunications and Information Administration (NTIA) plan to assess this summer,” they wrote.

Foxx said Tuesday that he wants his department and the FCC to continue to evaluate the pros and cons of sharing 5.9 GHz in an orderly fashion.

“The proponents would open up some of that spectrum so that you could make multiple uses of it,” Foxx said. “From our vantage point, it’s unproven for this type of use. So what we’ve proposed, and we’ve gotten agreement from the FCC and NTIA to do, is to actually conduct an experiment to determine definitively whether spectrum sharing can occur safely.”

Foxx continued: “It’s disappointing that some of the consumer electronics industry has now gone to, instead of giving us some potential technologies to try within that study, are now trying to disrupt the use of spectrum by challenging it at its foundation.”