US farmers have launched a fresh campaign to push back against President Donald Trump's upcoming tariffs on steel and aluminum imports, fearing foreign retaliation would seriously hurt their export-dependent industry.

Farmers for Free Trade, a nonprofit campaign, released a TV ad on Tuesday calling on Trump to protect the trade policies US farmers depend on.

In the ad, Michelle Erickson-Jones, a fourth-generation farmer and rancher from Broadview, Montana, and president of the Montana Grain Growers Association, voices her concerns about Trump's trade policy.

"We depend on free trade policies to maintain our export markets," she said in the 30-second ad that will be aired for at least the next four weeks on cable news networks such as Fox, CNN and MSNBC, as well as online and on rural agricultural programs.

"The crops that we grow here on this farm are exported across the globe. Policies that restrict trade would be devastating for farms like ours. Someday I'd like to pass the farm down to my boys. Mr. President, protect free trade and keep our agriculture economy strong," said Erickson-Jones, standing next to her husband, each holding one of their two young sons.

The ad kicks off Farmers for Free Trade's "Voice of the Farmer" campaign, which has already posted a number of videos on its website featuring farmers from various states calling for free trade.

Former Montana senator Max Baucus, who was US ambassador to China during 2014-17, and former Indiana senator Richard Lugar were co-chairs of the campaign.

"Farmers are increasingly worried about what they are seeing from Washington D.C. on trade," Baucus was quoted as saying in a news release.