Surveillance laws are not fit for purpose and need to be overhauled, a group of MPs have said.
Police officers are failing to routinely record the professions of individuals who have had their communications data accessed under the Regulation of Investigatory Powers Act (Ripa), the Home Affairs Select Committee said in a report.
The comments come after it emerged police investigating the Chris Huhne speeding points scandal secretly obtained the phone records of a journalist and one of his sources for the story, even though a judge had agreed that the source could remain confidential.
And it was previously revealed that the Metropolitan Police used the Act to obtain The Sun's newsdesk telephone records and those of its political editor, Tom Newton Dunn, to try to identify who had leaked the so-called Plebgate story involving former Tory chief whip Andrew Mitchell.
Keith Vaz MP, chairman of the committee, said: "Ripa is not fit for purpose. We were astonished that law enforcement agencies failed to routinely record the professions of individuals who have had their communications data accessed under the legislation.
"Using Ripa to access telephone records of journalists is wrong and this practice must cease.
"The inevitable consequence is that this deters whistleblowers from coming forward.
"The recording of information under Ripa is lamentably poor, and the whole process appears secretive and disorganised, without proper monitoring of what is being destroyed and what is being retained.
"We are concerned that the level of secrecy surrounding the use of Ripa allows investigating authorities to engage in acts which would be unacceptable in a democracy, with inadequate oversight."
The Committee called on the Home Office to hold a consultation on an amended Ripa Code of Practice with special provisions for dealing with privileged information, such as journalistic material.
Earlier this year, Sir Paul Kennedy, interim Interception of Communications Commissioner, lau nched an inquiry into potential misuse of Ripa following reports forces used the legislation to access reporters' telephone and email records.
Shadow home secretary Yvette Cooper said: "Labour has said for some time that Ripa needs to be reviewed - that is why we insisted on a statutory review as part of the Government's legislation on data retention in July.
"The law hasn't kept pace with advancement in technology and it needs to be proportionate. Access to communications data is vital to the police and intelligence agencies in their fight against terrorism, child abuse and other serious crimes.
"But it is also important that there are strong checks and balances in place to ensure this data is not used inappropriately.
"That's why we need to implement the review by David Anderson which the Labour Party called for earlier this year, which must look at worrying reports that journalists' data is being accessed to uncover their sources.
"Other parts of the law such as the Police and Criminal Evidence Act have extra safeguards in them to protect a free press - there should be similar safeguards for communications too. Journalists should not be above the law, but nor should investigative powers be used in a way that has a chilling effect on free speech."
Immigration and Security Minister James Brokenshire said: "A free press is fundamental to a free society and the Government is determined that nothing is done which puts that at risk.
"Communications data is an absolutely critical tool used by police and other agencies to investigate crime, safeguard national security and protect the public. There are measures in place to ensure that police powers to access this data are not abused.
"We have also been working to strengthen the relevant code to ensure extra consideration should be given to a communications data request involving those in sensitive professions, such as journalists.
"We anticipate that the revised code will be published before Christmas and that full public consultation will take place."
A privacy lobby group said the current situation was "intolerable".
Emma Carr, director of Big Brother Watch, said: "When a senior parliamentary committee says that the current legislation is not fit for purpose, then this simply cannot be ignored. It is now abundantly clear that the law is out of date, the oversight is weak and the recording of how the powers are used is patchy at best. The public is right to expect better.
"Whilst this report concentrates on targeting journalists, it is important to remember that thousands of members of the public have also been snooped on, with little opportunity for redress. If the police fail to use the existing powers correctly then it is completely irresponsible for the Home Office to be planning on increasing those powers.
"Failure by the Government to address these serious points means we can already know that there will be many more innocent members of the public who will be wrongly spied on and accused. This is intolerable."
Isabella Sankey, director of policy for Liberty, said: "The secret use of Ripa to investigate journalists' sources will chill anyone who values free speech and a free press. But what's disturbing is that the abuses detailed in this damning report are the tip of the iceberg.
"Records about your phone calls and emails builds up an incredibly detailed data-picture of every single one of us - who we are, where we go, what we do.
"We urgently need safeguards to stop this valuable data being accessed without judicial warrant. What we're getting is the Government handing itself even more powers to snoop, in the form of the ill-targeted Counter-Terrorism and Security Bill."