Trinity Mirror shares have fallen 28% in London after the group warned that full year operating profits will be 10% lower than expected.
The publisher behind the Daily Mirror, the Daily Record, the People and 150 regional titles blamed deteriorating conditions in the advertising market.
It has also decided to cancel £67m of its £175m share buyback programme.
It blamed the uncertain economic outlook, rising costs and "the wider implications of the credit crunch".
Trinity Mirror's shares closed down 42.5 pence, or 28.1% at 109p.
"We have seen a marked year on year decline in advertising revenues across our businesses during May and June and this is expected to continue for the remainder of the year," the group said in its announcement to the London Stock Exchange.
In addition to cancelling the remainder of its share buyback programme, the group said it would have to consider the appropriate level for its dividend when trading conditions had become clearer.
Its half year results are due to be announced on 31 July.