Politically-embarrassing requests could be buried more easily if proposed changes to the Freedom of Information are put through, say campaigners.
About 10% of requests come from journalists
The £600 limit on processing requests may be extended to include officials' time, the Lord Chancellor suggested.
The Campaign for Freedom of Information said it would make it easier for authorities to refuse potentially embarrassing requests on cost grounds.
The government has said the changes could save £5m of taxpayers' money.
Requests are already rejected if it costs more than £600 to process them - but Lord Chancellor Lord Falconer has now suggested including the cost of ministers' and officials' time in dealing with requests to be included in that cost.
But the Campaign for Freedom of Information director Maurice Frankel said ministers chose to involve themselves in potentially "newsworthy" requests - and their time was the most expensive.
He told the BBC: "By all means, let them do it, but don't allow the fact that they choose to become involved to count towards the costs."
He added: "By doing this, what they are actually going to do is make it much easier for authorities to refuse on costs grounds.
"It would reduce the amount of politically-sensitive and politically-embarrassing information that would be disclosed."
Multi-million pound cost
Phil Michaels, of Friends of the Earth, added: "That's likely to have the effect that public authorities are going to be able to play for time, and essentially knock requests out, simply on the basis that it would take them too long to deal with."
A review of the impact of the act found requests cost central government £24.4m a year and other public authorities £11.1m a year.
Central government was expected to receive 34,000 requests under the act a year, 10% of which were journalists' requests - which tended to be the most time-consuming.
The Department for Constitutional Affairs report said including officials' time in the £600 limit would mean 8% fewer requests - saving £4.7m a year.
Another proposal suggests a series of requests from the same organisation - even on different topics - could also be considered as one request and refused on cost grounds.
This would lead to a further 11% fall in the number of requests, saving just under £1 million a year, the report said.
But information rights minister Baroness Ashton told the BBC Radio 4's World At One programme the government had always intended to review the Act within 18 months.
She said it was "right and proper" that the cost to the taxpayer was considered, and rejected the idea that politically embarrassing questions would automatically be rejected.
"I don't think that's the case at all. It's a case of looking at when we spend £25m of tax payers' money in central government, how best we can make sure that money is used effectively and make sure that we deal with requests efficiently."
The government has rejected the idea of a flat-rate fee to submit an FOI request.
Lord Falconer added: "It would be wrong not to make adjustments in light of experience and make sure we get the balance right between the provision of services and the provision of information."
But shadow constitutional affairs secretary Oliver Heald said it was "a stealth attempt to curtail the right to know and hinder individuals from asking for information to which they are entitled."
Liberal Democrat legal affairs spokesman Simon Hughes said the changes could "greatly undermine" increased openness, accountability and trust in the work of public authorities.