The NUJ has condemned the Government for overturning amendments made in the Lords to the Defamation Bill and adding others which the union says back the interests of big business over press freedom.
The union said the bill had enjoyed cross-party support and a wide consensus outside Parliament, but the government has spurned the chance of bringing the UK's libel laws up to date.
It claims amendments will severely water down the bill and scupper important changes which offer journalists greater protection against corporations which use the threat of a costly libel action and lengthy proceedings to close down criticism of their products or practices.
Chris Frost, chair of the NUJ's ethics committee, said: "This is an important bill for journalists and all citizens. Our present libel laws are ones which suit only the rich and powerful and hamper investigative journalism and free speech. The amendments made in the House of Lords were important improvements and it is outrageous that the government has decided to back the interests of big business over press freedom."