A Welsh Labour minister has accused Plaid Cymru leader Adam Price of using "deliberately offensive terminology" comparing the experience of Wales with colonialism.
Vaughan Gething's comments follow an interview in which Mr Price said Wales had suffered a "century of neglect".
Mr Price had argued that Wales had an "extractive economy" and "political power centre outside of our nation".
This was "analogous if not identical" to the colonial experience, he said.
Mr Price said it was a "deliberate attempt to distract from the real issues" by "smearing" him, and described it as "ugly politics".
He said: "We're suggesting some solutions to Wales' problems, what the Labour Party is trying to do is distract away from its responsibility as the party that's been in government in Wales for 20 years."
In the interview, with the think tank the Institute of Welsh Affairs, Mr Price said Plaid Cymru wanted "reparation for a century of neglect that has left a country, rich in its resources, a bitter legacy of poverty, sickness, blighted lives and broken dreams".
He said: "I feel very strongly that it's not possible to understand the predicament we're in without acknowledging the centrality of the fact that we had an extractive economy with a political power centre outside of our nation.
"For most people that is analogous if not identical to the experience of colonialism."
Mr Price continued: "The term internal colonialism was invented to describe the experience of African Americans in the United States.
"In fact, there is a quote from the 19th Century where they were referencing our experience - the Welsh inside the British Isles - in order to explain their own experience of internal colonialism.
"I don't think you can understand the predicament we've been left in without those two salient facts and the inter-relationship between the two."
Responding, Mr Gething called on Mr Price to apologise.
The minister told BBC Radio Wales Breakfast he was "pretty staggered that he's chosen to use such deliberately offensive terminology that directly references the experience of Wales and colonialism, and further back slavery".
"You just cannot compare the experience of Wales in the 19th and 20th Centuries with the experience of the emancipation campaign from slavery or indeed the state-backed racism that was visited upon African Americans in America," he said.
Mr Gething said Wales itself had a direct role in the history of slavery.
"There's no surprise that some of the most popular African American surnames are Welsh ones," he said.
"And that's because, when they were finally given their freedom, they were given the names of their slave owners."
"To try to say that the experience of Wales as a country and as a people is analogous to colonialism, is analogous to slavery, that is just outrageous," he said.
Mr Gething also referred to his mother, who was born in the British colony of Northern Rhodesia, that became Zambia.
"Her experience growing up, and her family's experience growing up, was not like the experience of Wales in the 19th and 20th Century," he said.
Mr Price said he found it insensitive to suggest or create the impression that he was a racist, and "we need to park these personal insults and let's talk about the issues".
A Plaid spokesperson added that the Labour Party in Wales had been "failing to deliver on the economy, healthcare and education - all things under their control" .
"Labour should really be spending more time trying to fix the position Wales finds itself in," the spokesperson said.
"The fact that a third of our children living in poverty is a direct result of the kind of economy we have which has extracted from Wales without allowing our nation to benefit, with power centralised outside our own country."