"The House-approved plan's "Buy American" provision generally prohibits the purchase of foreign iron and steel for any infrastructure project in the bill.
The European Union's trade commissioner, Catherine Ashton, pre-emptively voiced concern about the US measure.
"We are looking into the situation. ... Before we have the final text ... it would be premature to take a stance on it," Ashton's spokesman, Peter Power, said in Brussels.
"However, the one thing we can be absolutely certain about, is if a bill is passed which prohibits the sale or purchase of European goods on American territory, that is something we will not stand idly by and ignore," he said.
Canada's government said it is concerned about US protectionism in the economic stimulus and its diplomats were lobbying US makers against the "Buy American" drive.
"We're always concerned when there are protectionist pressures in the United States," Industry Minister Tony Clement told public broadcaster CBC.
"At the same time the United States has treaty obligations," he said, citing US membership in the World Trade Organization and the North American Free Trade Agreement (NAFTA).
"And we expect the United States to live up to its treaty obligations of open and fair trade."
About 40 percent of Canadian steel is sold in the United States and Canada imports steel from its southern neighbor."