Manufacturing—and steel—support for Senate legislation aimed at tackling the undervaluation of the Chinese yuan is gaining strength, with a chorus of leading voices are getting behind the bill.

In the past week, a bipartisan group of U.S. senators has introduced legislation and more than 130 members of Congress have signed a letter urging the Obama administration to support the Currency Exchange Rate Oversight Reform Act, a bipartisan effort by Sen. Charles Schumer (D., N.Y.), Sen. Debbie Stabenow (D., Mich.) and Sen. Lindsey Graham (R., S.C.).

"The continuing and deliberate undervaluation of currency by foreign governments, in particular China, is one of the most pernicious of unfair trade subsidies," Leo W. Gerard, president of the United Steelworkers union, said. "Currency undervaluation has contributed substantially to the loss of millions of American manufacturing jobs in the past few years."

The union leader said that China continues...