WASHINGTON—Senate Minority Leader Chuck Schumer (D., N.Y.) told President Trump his preliminary trade agreement with China doesn’t go far enough, warning that the deal could produce little benefit for American companies and workers, while also emboldening Beijing.

Mr. Schumer, in a letter to the White House released Tuesday morning, said U.S. businesses stand to lose billions of dollars if the administration can’t secure concrete commitments from China to stop subsidizing domestic companies and sponsoring efforts to steal intellectual property, among other changes. Making a temporary deal could concede leverage the U.S. needs to pressure China, Mr. Schumer said.

President Trump has enjoyed rare bipartisan support for his trade war with China, and Mr. Schumer’s letter could signal that period coming to an end. Mr. Schumer has long backed a hard-line approach to Beijing and sought to discourage trade-friendly officials in the Trump administration from caving to Chinese demands. Last May, when Mr. Trump announced a major increase in tariffs, Mr. Schumer responded quickly with a tweet of support, urging the president to “hang tough on China.”

“From what I understand from reading press reports, the terms of the agreement will result in very little progress in reforming China’s rapacious trade behaviors and seems like it could send a signal to Chinese negotiators that the U.S. can be steamrolled,” Mr. Schumer said in his letter, dated Monday.

Mr. Trump is gearing up for a White House ceremony scheduled for Wednesday to sign a compromise deal with Chinese leaders. The accord promises increased purchases of U.S. goods and services, greater access for American companies to China’s banking, insurance and other financial sectors and an end to tariff threats.