Plaid Cymru is being urged to removed its candidate for Ceredigion because he wrote an article claiming that "many English migrants into rural Wales are out and out racists".
Mike Parker also suggested that they were "leaving English cities to get away from multi cultural society".
Mr Parker made the remark in an article in 2001 when he was working as a travel writer.
In the piece he said rural Wales had become the "British equivalent of the American mountains inhabited by a sprinkling of paranoid conspiracy theorists, gun-toting Final Solution crackpots and anti-government obsessives".
In the article he went on to say, "Add to these the thousands of small-minded Little Englanders who have transferred their phobias from the black and Asian populations of their native cities to 'the Welsh' or 'the Taffia' in their new locales, and there is room for much ill-feeling and even trouble."
The party has said Mr Parker now recognises the language he used was "inappropriate".
He added in a statement that he would no longer use such "high octane" vocabulary to express himself, but insisted racism should always be challenged.
The party is now being urged to deselect him as its candidate for the seat.
Nicola Hendy reports from Aberystwyth:
Labour candidate Huw Thomas called the comments "outrageous and deeply offensive" and "exactly the sort of poisonous rhetoric you'd expect from Ukip".
Liberal Democrat Peter Black, who sits in the Welsh Assembly, said Plaid's leader Leanne Wood needed to "show some leadership" and demand a full, public apology from Mr Parker.
The Welsh Conservatives said the comments were "very concerning" and called for a full investigation.
Gethin James, who is contesting the seat for Ukip, said that if a member of his party had written such a "derogatory" article they would have been asked to consider their position.
In his statement, Mr Parker said he had been seeking to understand more about what had drawn people to move to rural Wales at the time.
He added, "I knew my own reasons why - this is a part of the world that had always fascinated me. Moving here, I felt instantly at home thanks to the tolerant and compassionate community here.