Cabinet minister Michael Gove accused Sir Keir Starmer of planning to “downgrade the ultimate privilege of British citizenship” by giving EU nationals in the UK the right to vote in a general election.
The Labour leader has suggested people who have spent decades living in the UK ought to be able to vote in elections to decide who runs the country.
But Levelling Up Secretary Mr Gove wrote to the Labour leader saying it had been the “settled constitutional position for many decades” that the right to vote in a general election was limited to British, Irish and qualifying Commonwealth citizens.
He also hit out at the prospect of Labour lowering the voting age to 16, arguing that “adulthood begins at 18”.
Labour is looking at proposals to extend the franchise for general elections, but has not yet fixed on a policy.
Opponents have accused Labour of seeking to undermine Brexit and rig the voting system, in the belief that younger voters and EU nationals may be more inclined to support Sir Keir’s party.
In his letter to Sir Keir, Mr Gove said: “Why do you think we should extend voting rights to EU nationals (which they never previously had), now we have left the European Union?
“Why do you think it’s right to downgrade the ultimate privilege of British citizenship – the right to vote in a General Election?
“What do you say to those who say that your approach is designed to undermine Brexit – and ‘rig’ the voting system for national elections and referendums?”
Speaking on LBC on Monday, Sir Keir said: “If someone has been here say 10, 20, 30 years, contributing to this economy, part of our community, they ought to be able to vote.”
He added that the fact settled migrants do not have full voting rights “actually just doesn’t pass the common sense test for me”.
Allowing teenagers aged 16 and over to cast a ballot is also “not such an outlandish idea”, Sir Keir said.
He pointed to Wales where the voting age for Senedd and local government elections has been lowered to 16.