WASHINGTON (AP) — President Donald Trump's plan to privatize the nation's air traffic control system is running into bipartisan opposition in Congress, where Republicans fret that it could raise costs for air travelers and hurt small airports.

Sen. Roger Wicker, R-Miss., called the proposal "a tough sell" in states like his, where small airports are common. At a hearing Wednesday, Wicker told Transportation Secretary Elaine Chao that "the sale needs to be made, and it needs to be made convincingly" if the administration hopes to move forward with a plan that U.S. airlines and some House Republicans have long advocated.

Sen. Jerry Moran, R-Kan., said privatization would hurt "all but our largest airports nationwide," while removing needed congressional oversight and raise costs for consumers.

Democrats also opposed the changes, warning that airline interests would dominate a proposed board that would oversee an estimated 300 air traffic facilities and around 30,000 employees.

Lawmakers from both parties also pointed to the unprecedented safety under the current system, noting the last fatal crash of a domestic passenger airliner was eight years ago.

"We currently have the safest air-traffic control system in the world. Why risk that by handing the whole thing over to an untested, unproved entity?" asked Florida Sen. Bill Nelson, the senior Democrat on the Senate Transportation committee.

While the U.S. "remains the gold standard in aviation," the president's plan would spur innovation and modernization, Chao said.

"Our skies are becoming increasingly congested," she said, noting that some domestic flights take longer now than they did decades ago because of congestion and indirect routing.

"Our air traffic organization must be more nimble," Chao said, calling the current system "bulky" and unable to "move fast enough to keep pace with new technologies and new demands."

But Nelson and other Democrats noted repeated computer system failures in recent years by U.S. airlines, questioning whether they are ready to handle complex technology modernizations.

Business aircraft operators, private pilots and nonhub airports have also expressed concerns that they may pay more and receive less service under a private corporation.

U.S. airlines have lobbied to separate air traffic control from the Federal Aviation Administration for two decades, and Trump's budget plan released earlier this year called for the changes, placing air traffic operations under an "independent, nongovernmental organization."