All three major U.S. stock indexes posted gains on Friday despite concern that the Trump administration's decision to impose new tariffs on China marked the start of a trade war.

The blue-chip Dow Jones industrial average rose 0.39 percent at the end of New York trading, while the tech-heavy Nasdaq gained 1.3 percent and the broader S&P 500 added 0.84 percent.

The U.S. trade representative began assessing duties of 25 percent on $34 billion worth of Chinese products on Friday and is considering adding them to an additional $16 billion in goods. President Trump has threatened to increase that amount to as much as $500 billion, and China – which immediately retaliated for the initial levies – said it would respond in kind.

The administration previously imposed a 10 percent tariff on aluminum imports and a 25 percent tariff on steel imports. The European Union, Mexico, and Canada have all struck back, scoffing at the White House's use of national security concerns to justify the charges.

Businesses are worried that the administration's trade agenda will undermine a growing economy and blunt the positive impacts of the GOP-led tax cuts. The U.S. Chamber of Commerce launched a campaign opposing the tariffs, and the National Association of Manufacturers warned that the tariffs could hurt American factories, which typically offer higher-paying jobs, the most.

The U.S. added 213,000 jobs in June, a signal that the economy has not yet suffered from the brewing trade war.