OTTAWA (Reuters) - Canada will hit back against U.S. tariffs on its steel and aluminum by offering affected companies and workers up to C$800 million ($603 million) in aid, a source familiar with the matter said on Thursday.

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Foreign Minister Chrystia Freeland will make an announcement in the steel city of Hamilton at 11 a.m. ET (1500 GMT) on Friday.

The source, who declined to be identified because of the sensitivity of the situation, said Freeland will announce the aid and reveal a list of U.S. goods that Canada intends to subject to retaliatory tariffs.

U.S. President Donald Trump imposed tariffs on Canadian steel and aluminum last month, citing national security reasons. The move helped upend one of the world’s most important trading relationships and soured ties between Ottawa and Washington.

Freeland said on June 19 that the Liberal government of Prime Minister Justin Trudeau was working on ways to directly support the steel and aluminum industries and their workers.

Freeland’s office did not immediately respond to a request for comment.

The source said the assistance - to be spread over several years - would be similar to an C$867 million five-year package offered to Canadian softwood lumber producers in 2017 after Washington imposed tariffs.

That took the form of loans, loan guarantees, commercial financing and support to help firms expand overseas markets. It also included money to help affected workers learn new skills and provided support for work-sharing agreements.

The source did not say which steel and aluminum firms would be in line for help. Companies with operations in Canada include Evraz Plc, Rio Tinto Plc, Algoma Acquisition Corp [ALGMA.UL], Essar Steel Algoma Inc [ESSRGE.UL], ArcelorMittal SA and Alcoa Corp.

Canada promised to react by imposing retaliatory tariffs on C$16.6 billion worth of U.S. exports and Freeland is due to outline exactly which goods will be hit, said the source.

Trump is also threatening to impose tariffs on Canadian autos, which would cause significantly more economic harm.

Senior officials from Canada are lobbying the Big Three U.S. car makers to stave off the punitive measures and say they are considering all options, including providing financial aid.