The Republican president's hefty tariffs on Canada have caused friction with the US neighbour to the north while creating problems for American businesses in Maine and other states that rely on certain Canadian goods.
With the November 3 US midterm elections looming and Republicans fighting to retain control of Congress, Senator Susan Collins had urged the White House to address tariffs on products affecting Maine companies and farmers.
Trump's order exempted plywood sheets, some paper products, certain machinery and refrigeration equipment, and packing crates and boxes, as well as fresh and dried seaweed, the White House said.
The changes take effect on October 30, four days before the election.
Trump added a number of Canadian products to the 50 per cent tariff list to offset the tariff relief provided in his order, including carpets, paints, shampoos, cocoa powder, wooden coffins, ice cream sticks, air-conditioning machines, chest freezers, archery equipment and canoes.
Collins said the relief will aid Maine's blueberry, potato, apple and seaweed producers.
"These producers are a vital part of our state's economy and support our rural and coastal communities," she said.
"Many of our farmers and growers rely on specialised equipment, packaging materials and other products from Canada that are either unavailable from American suppliers or cannot be replaced without incurring significant expense."
Democrat Troy Jackson is seeking to oust Collins in next month's election in a race that polls indicate is very close.
Trump in August imposed 50 per cent tariffs on $US20 billion of Canadian imports, which took effect after talks between the two countries collapsed. Canada retaliated in September with tariffs ranging from 15 per cent to 50 per cent on $US20 billion in US goods.
Canada and the United States have been engaged in a standoff over the tariffs since Trump imposed them. Trump on Friday asserted that Canada is working on a deal.
Republican candidates in northern US border states most affected by the tariffs, including Maine and Michigan, are trying to strike a balance between appealing to Trump's loyal conservative base and winning over independent voters.
In a statement concerning Trump's action, White House spokesperson Matthew Middleton said the president "continues to address Canada's discriminatory treatment of US commerce" and that the new moves are "further refining the scope" of the previously announced tariffs.
The Canadian embassy in Washington did not immediately respond to a request for comment.
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