A Plaid Cymru Senedd election billboard has been accused of being a "riff" on a racist campaign slogan from the 1960s.
Candidate Carrie Harper's advert said: "Don't want a Tory for a neighbour? Vote Plaid Cymru, not Labour."
Labour said it was "inspired by the racism of Smethwick" - referring to a Tory campaign slogan in the English west midlands seat in 1964.
Ms Harper, standing in Wrexham, said she deeply regrets the "language used has unintentionally caused offence".
She said that was "in no way the intention".
In a statement the Wrexham councillor said the advert, withdrawn before the weekend, had "included the word 'neighbour' to reference the fact that the billboard was next to the office of the Conservative MP".
"I want to focus on a positive campaign aimed at delivering real change for the community where I grew up and live," she added.
In a Twitter comment on Thursday night, Welsh Labour said: "Either Plaid are naive and don't know what this sounds like or it's a dogwhistle and they don't care.
"Riffs on Smethwick 1964 slogans should stay in the past."
Labour's Lesley Griffiths is defending the seat.
WALES ELECTION: THE BASICS
What elections are happening? On 6 May, people across Wales will vote to elect 60 Members of the Senedd (MSs). The party or parties that can command the support of a majority of members will form the Welsh government. Find out more here.
What powers does the Welsh Parliament have? MSs pass laws on many aspects of day-to-day life in Wales, such as health, education and transport. They also have control over some taxes. Defence, foreign policy and immigration are decided by the UK Parliament.
How do I vote? Anyone who lives in Wales and is registered to vote is eligible, so long as they are aged 16 or over on the day of the election. You can register to vote online.
A Welsh Conservative spokesman said: "This is an insult to over a half million people who voted Welsh Conservative in 2019.
"If the people of Wrexham want change after 22 years of Labour Government in Wales, and a decent, hard working local MS, they should vote for Jeremy Kent."
Tim Sly, Welsh Liberal Democrat candidate in Wrexham, said: "Slogans like this are horrible, divisive and have no place in politics and those responsible for writing and sharing this slogan should be ashamed.
"Serious questions also need to be asked about the judgement of those who chose this slogan and their suitability to stand for office."
Other candidates standing in Wrexham are:
- Reform UK - Ian Berkeley-Hurst
- Abolish the Welsh Assembly Party - Paul Ashton
- UKIP - Sebastian Ross
- Gwlad - Aaron Norton