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An upcoming bill will bar EU citizens resident in the UK from voting in the EU referendum.
But David Cameron's plans to exclude 16- and 17-year-olds from the vote have angered critics.
Labour and the SNP have now said they will seek to amend the EU Referendum Bill when it is introduced on Thursday.
Shadow foreign secretary Hilary Benn said:
If a person aged 16 or 17 is old enough to work, to pay taxes, to marry, to join the armed forces, why should they not be able to participate in our democracy?
The SNP permitted 16- and 17-year-olds to vote in the Scottish referendum last year, and the move was hailed as a success in encouraging greater political engagement among youngsters.
More: [Here's a list of all the people who can vote in the EU referendum, and those who can't]2