Elis Owen said it was "appropriate" to move on after 30 years
Concern has been voiced by Welsh Assembly Government Heritage minister Alun Ffred Jones over a management restructuring at ITV Wales.
The restructuring means ITV Wales national director Elis Owen is leaving after 30 years.
Mr Jones called it an "erosion of ITV Wales' independence and programme-making" which was "very worrying".
ITV said it had a "strong management team" to lead it through an important period for public service broadcasting.
Mr Jones said he feared Wales' voice would be "diluted" by a merging of roles to create a senior director for ITV Wales, Granada and Central.
ITV said its changes would mean Phil Henfrey, currently head of news at ITV Wales, will become head of news and programmes and become the senior executive at the broadcaster's Cardiff base.
He will report to Mike Blair, the director of ITV Wales, Granada and Central.
Jonathan Hill, currently presenter of news programme Wales Tonight, will become associate editor of ITV Wales, in addition to his existing on-screen role.
But Mr Jones said he feared an impact on the level of news and non-news programming produced by ITV Wales.
"Wales needed a strong independent voice in broadcasting to provide a counterbalance to the provision of BBC Wales and this makes the expected statement at Westminster on digital Britain even more important," said Mr Jones.
He added: "We need to maintain and increase plurality in broadcasting here in Wales.
"The fact that the senior ITV executive in Wales will now report to a new director of ITV Wales, Granada and Central is not a step forward for broadcasting in Wales."
ITV controller of regions and current Affairs Ian Squires said: "I'm delighted that we have such a strong management team to lead ITV through an important period for the future of public service broadcasting in the nations and regions.
"Elis has made a significant and lasting contribution to television production in Wales. He is a wonderful champion for the industry in the nation. We wish him well and hope his advocacy will long continue."
Mr Owen said: "ITV is restructuring the management in the English regions and Wales, therefore, I have decided that this is an appropriate time to move on. I have always been passionate about programmes and production in Wales in both English and Welsh and I will continue to be so."
The other two ITV directors will cover Yorkshire, Tyne Tees & Border and Anglia; and West & West Country, Meridian and London.
Meanwhile, Conservative heritage spokesman Alun Cairns said he was "extremely concerned".
He added: "This announcement fails to accept the concept of nations within the United Kingdom and is a further 'salami slicing' of the broadcaster in Wales following recent cuts."
Mr Cairns said the timing was also "nonsensical" given that the department of culture, media and sport and Ofcom were looking at ways to support ITV Wales and "secure plurality of news and non-news broadcasting".
"Today's announcement essentially downgrades ITV Wales to regional status on a par with those in England."