Liberal Democrat Peter Black, left, who represents South Wales West in the Welsh Assembly, said he was concerned that journalist jobs in the area could move from Swansea to Cardiff if a merger goes ahead.
Trinity Mirror confirmed last week that it was in talks to buy out the 80pc of shares in Local World that it does not already own.
If the £200m deal goes ahead, it would mean that Trinity Mirror would own three of the four daily titles in South Wales – the South Wales Echo, the Western Mail and the South Wales Evening Post – along with the North Wales Daily Post and a clutch of weeklies.
Mr Black said: “Trinity Mirror has centralised all its operations in Cardiff, closing branch offices in Merthyr Tydfil, Bridgend and Pontypridd in the last year.
“In the process they have forced staff to work from home or in their Cardiff headquarters.
“We need assurances from Trinity Mirror that if this takeover goes ahead, then they will keep offices in Swansea, Llanelli and Carmarthen open, maintaining the important link between locally-based papers and the communities they serve.
“I am also concerned at possible redundancies as a result of this takeover. That is why I have asked the Minister to engage with Trinity Mirror to press them on this issue and to try to minimise job losses.”
A spokeswoman for Trinity Mirror said the company was unable to comment.