A fight over fuel efficiency is looming. The Trump administration has been holding public hearings this week on its plan to undo Obama-era regulations. 

States like California are threatening to go to court. 

And even in Arizona — a place that's no friend of federal regulations — there’s concern about public health if the proposal goes forward.

It didn’t take long for Columba Sainz to notice the air quality after moving to Phoenix.

“Seeing my daughter wheezing at night, waking up, having trouble to breathe,” Sainz says. “It just gave us a red flag.”

Sainz discovered the symptoms were, in part, tied to the pollution in her downtown neighborhood. She began advocating for better air by speaking to other families in the community.

“We talk about cars. We talk about the quality of the air. We talk about climate change,” Sainz said.

It’s a conversation now happening across the country as the Trump administration moves to weaken the fuel efficiency standards for new cars.

This could be a big problem for the Phoenix metro area. The Valley struggles with pollution and transportation is a major source. But Will Humble, the former director of the Arizona Department of Health Services, says it has been getting better.

“Smog, our particulate matter, ozone, carbon monoxide, if you go down the list, air quality is improving,” Humble said.

He cites intervention of the fuel efficiency standards that took effect in 2012, which require new cars to get more miles per gallon.

“One of the reasons why air quality has been improving is that the efficiency of vehicles has been getting better.”

The standards are set to keep going up in the coming years. But the Trump administration hopes to freeze these increases after 2020. It argues the standards are driving up prices, and the proposed changes will let more consumers buy new, safer cars.

Some states are vowing to fight the effort in court.

Arizona isn’t doing that, but it is quietly opposing the changes. A letter from the state’s head of air quality to the federal government cites concerns about high ozone levels — only projected to get worse in coming years.

“It does hit close to home," said Ram Pendyala, who studies transportation at Arizona State University.

He says the Obama-era standards have made a big difference in the car industry.

“It has has spurred innovation. It has motivated auto manufacturers to invest in hybrid vehicles, more fuel efficient engine technology.”

Automakers echoed this sentiment at this week’s public hearing in Michigan, when executives from Ford and Fiat Chrysler said they’re committed to making more fuel efficient vehicles.