A series of anti-monarchy billboards have been described as "offensive" ahead of the Queen's Platinum Jubilee.
Reading-based campaign group Republic raised £43,000 through crowdfunding to print and display the posters with the slogan "Make Elizabeth the Last".
Its chief executive, Graham Smith, said it was "absolutely the right time to raise the issue and get people debating the future of the monarchy".
But Reading councillor Clarence Mitchell said it was "disgraceful".
Republic said on its website the first tranche of billboards would go up in Reading, Manchester, Bournemouth, Birmingham, Dundee, Leeds, Glasgow, Newcastle and Bristol.
Mr Smith told the BBC: "Seventy years of one person being head of state is not a great idea.
"It's not healthy for a democracy and this is also probably the last major event of the Queen's reign and we need to start thinking about what's going to happen next."
The latest figures from YouGov, which tracks public opinion, show 61% of people in the UK support having a monarch, while 24% would prefer to have an elected head of state.
There has been a change in opinion over the last few years among 18 to 24-year-olds.
In 2019, 46% of that age group were in favour of having a king or queen and 31% wanted to have an elected figurehead.
By 2021, 31% supported the monarchy while 41% wanted to be able to vote for a head of state.
Mr Mitchell said the timing of Republic's stunt "is as disgraceful as it is distasteful and sadly it's tediously predictable".
He added: "In a democracy, under a constitutional monarchy, Republic can make all the arguments they want and they have every right to do that.
"But this sort of stunt, offensive as it is, is going to alienate far more people than it brings towards their cause."