U.S. President Donald Trump speaks at the debut of the Boeing South Carolina Boeing 787-10 Dreamliner in North Charleston, S.C., 17, 2017.
U.S. President Donald Trump speaks at the debut of the Boeing South Carolina Boeing 787-10 Dreamliner in North Charleston, S.C., 17, 2017.

WASHINGTON - President Donald Trump visited a Boeing aircraft factory in South Carolina on Friday, just days after workers there rejected a bid to join the International Association of Machinists and Aerospace Workers.

Trump saw the rollout of a new version of a wide-body jetliner, the Boeing 787-10 Dreamliner. Boeing announced Thursday that Singapore Airlines had committed to buying 10 of the huge planes, which can seat more than 300 passengers.

During remarks to Boeing employees, the president said companies that fire American workers and move overseas "will pay a heavy penalty." Trump also said the U.S. military is looking at "a big order of F-18 Super Hornets."

He also said the U.S. military might buy Boeing fighter planes rather than those of rival Lockheed that he has called "overpriced."

WATCH: Trump remarks at Boeing

Trump told thousands of Boeing workers that he was elected to take care of "jobs, jobs, jobs" and pledged to push companies to keep work in the United States.

"Our goal as a nation must be to rely less on imports and more products made here in the U.S.A., right here in the U.S.A."

The nearly 3,000 workers who build Dreamliners at the North Charleston facility were eligible to join the union, but three-quarters of them voted against the measure after a long and hard-fought campaign pitted union organizers against the company.

Each side accused the other of lies and distortions in a campaign fought on television, online and in the workplace.   

WATCH: Trump tours factory

Joan Robinson-Berry, vice president and general manager of Boeing South Carolina, wrote that Boeing workers "will continue to move forward as one team" and have "a bright future."

Union leader Mike Evans expressed disappointment that workers will "continue to work under a system that suppresses wages, fosters inconsistency and rewards only a chosen few.

Union strategy seen as key

An expert on labor relations from Cornell University, Kate Bronfenbrenner, said her research showed "that union victory or loss depends most on the union's strategy."  She said most companies follow similar, usually very tough steps in their fight to avoid unionization. The machinists, Bronfenbrenner said, needed an "all-out campaign" that was "really organized right" in order to win.  

South Carolina has the lowest level of union representation in the nation, at 1.6 percent. State officials say businesses are more likely to bring jobs to an area where companies don't have to cope with unions.

Patrick Brothers, left, smiles for the camera as W
Patrick Brothers, left, smiles for the camera as Wendell Bailey, takes his photo as the two Boeing employees wait with others for President Donald Trump to speak, Feb. 17, 2017, in the final assembly building at Boeing South Carolina in North Charleston.

Boeing says it's the largest aerospace company in the world, with 148,000 employees. Published reports said Trump might try to help Boeing sell planes overseas by supporting the U.S. Export-Import Bank, a government agency that guarantees loans and gives technical advice to U.S. exporters.  

The Ex-Im Bank has been under political attack by conservative Republicans in Congress, who say the bank gives out unfair government subsidies, mostly to large companies that do not need help.  

The bank's supporters say the agency's services are paid for by the firms that use them, and that the Ex-Im makes a profit that goes to the U.S. Treasury. They also argue that killing the Ex-Im Bank would leave the United States as the only major trading nation that does not offer such help to its companies.

After the speech, Trump flew to his Florida resort, Mar-a-Lago, for the weekend.

Watch: Trump Celebrates New Boeing Plane; Pledges Focus on Jobs

On Saturday, he is scheduled to hold a big rally in central Florida.

The South Carolina appearance comes just one day after the president held a free-wheeling, marathon news conference where he defended the sometimes tumultuous first four weeks of his campaign.