“The main kind of dilemma that companies face right now is just uncertainty,” said Craig Allen, the president of the US-China Business Council, which organized the letter. “Will the tariffs remain in place? Are they in place in perpetuity? What is the exclusion process to request an exemption from the tariffs? Nobody knows.” Mr. Allen said his group had organized the letter because it wanted to make sure that businesses’ views, in addition to those of labor and environmental groups, would be taken into account during the Biden administration’s China review.