From this Sunday (13 January), the price of the Sunday Mirror will increase by 5p to 95p, and the price of The People will rise by the same amount to 90p.
The cover-price strategy is markedly different to that of Trinity's rival News International, which is currently discounting the cover price of The Sun in the South-East.
Recent sales for the Sunday Mirror have been good, and in the November ABCs, its circulation rose by 2 per cent to 1,358,370. The People, however, has struggled. Its November sales fell by 10.5 per cent to 683,802.
The future direction of the paper has also been put under scrutiny after its editor, Mark Thomas, stepped down last November.
The Trinity Mirror cover price increases coincide with the relaunch of the News of the World's Sunday package, which includes a new-look Sunday magazine.
One agency press director said: "This is a very brave strategy to take, especially when you consider that the News of the World is launching its new magazine."