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Given a passage and a question, find the answer to the question based on the passage. The answer should consist of only one word that lies in the span of only one of the sentences in the passage.

Paragraph: As originally enacted , the Voting Rights Act also suspended the use of literacy tests in all jurisdictions in which less than 50 % of voting - age residents were registered as of November 1 , 1964 , or had voted in the 1964 presidential election . In 1970 , Congress amended the Act and expanded the ban on literacy tests to the entire country . The Supreme Court then upheld the ban as constitutional in Oregon v. Mitchell ( 1970 ) , but just for federal elections . The Court was deeply divided in this case , and a majority of justices did not agree on a rationale for the holding .
Question: when did congress outlaw literacy tests altogether as a prerequisite to voter registration

Output:
1970