WASHINGTON (Reuters) - The United States’ top transportation official on Wednesday promoted the Trump administration’s proposed privatization of the air traffic control system in the face of criticism from Democratic lawmakers and some Republicans.

U.S. House Committee on Transportation and Infrastructure Chairman Representative Bill Shuster (R-PA) (2nd R) takes a gentle ribbing from Senator Ted Cruz (R-TX) (R) and others, including U.S. Transportation Secretary Elaine Chao (L), former Transportation Secretary Elizabeth Dole (2nd L) and Vice President Mike Pence (3rd L), after Shuster asked U.S. President Donald Trump (seated) to sign autographs after Trump signed principles of proposed reforms to the U.S. air traffic control system during an event at the White House in Washington, DC, U.S. June 5, 2017. REUTERS/Jonathan Ernst

“Our air traffic organization must be more nimble,” U.S. Transportation Secretary Elaine Chao told the Senate Commerce Committee. “A bulky federal government procurement apparatus does not move fast enough to keep pace with new technologies and new demands.”

President Donald Trump on Monday unveiled the plan to modernize air traffic control and lower flying costs. Under the proposal, air traffic control would be spun off from the Federal Aviation Administration (FAA) and put under the aegis of a nonprofit entity.

Critics say the plan would hand control of a key asset to special interests and big airlines.

Senator Roger Wicker, a Mississippi Republican, said on Wednesday that small airports in his state oppose the plan. He said that after air traffic privatization in the United Kingdom airline passenger fees rose 30 percent. “This is a tough sell,” Wicker said.

Senator Jerry Moran, a Kansas Republican, said he remains “skeptical” of the idea of removing Congress from air traffic control oversight and handing it to a 13-member board.

The administration says it would not charge the private entity for the government’s air traffic control assets and would bar Congress from reviewing fees charged by the board.

Senator Bill Nelson, a Florida Democrat, opposes the proposal. “Why give away billions of dollars in government assets to an entity that will be governed in large part by the airlines?” he asked.

Nelson argued “a fundamental breakup of the FAA cannot advance when there are such strong divisions among aviation stakeholders and in Congress. It just won’t happen.”

Chao denied that the major airlines would control the board and said they would have just two seats on the board.

She also pledged to address rural concerns. One big issue is whether general aviation could face higher costs and access to airspace if a private board takes over.

Executives from United Airlines UAL.N, Hawaiian Airlines Inc [HAII.UL], American Airlines Inc AAL.O and Southwest Airlines Co LUV.N, all represented by the Airlines for America lobbying group, praised the Trump plan on Monday.

The FAA spends nearly $10 billion a year on air traffic control funded largely through passenger user fees, and has spent more than $7.5 billion on next-generation air traffic control reforms in recent years.

It is unclear whether privatization would speed the rollout of new systems such as satellite-based aircraft tracking that replaces ground radar dating back to World War Two.