New counter-terror powers designed to tackle the “vaguely defined” crime of hostile state activity threaten the protection of journalistic sources, campaigners for freedom of expression and the press have warned.

In a joint statement, nine organisations including Index on Censorship and Reporters Without Borders have called on the House of Lords to recommend significant amendments to the bill as it reaches the closing stages of its passage through parliament.

Unveiled by ministers in the summer, the counter-terrorism and border security bill proposes broad powers for border guards to stop and search individuals without suspicion on the grounds of tackling “hostile state” activity, and would criminalise travel to terrorist hotspots and the viewing of terrorist-linked material online.

It has received significant criticism from the cross-party joint committee on human rights, which warned that the legislation crossed the line on human rights and could restrict free speech and curb access to information.

Joy Hyvarinen, the head of advocacy at Index on Censorship, said: “The counter-terrorism and border security bill would change the law on freedom of expression in Britain, restrict press freedom, damage academic research and endanger fundamental rights. The bill is fatally flawed and we urge the House of Lords to ensure that the government rethinks the bill.”

The joint statement said the “vaguely defined” crime of hostile state activity introduced by the bill will give border guards wide-ranging powers to stop, search and detain.

The signatories said that a journalist taking a domestic flight could be stopped without any suspicion of wrongdoing and it would be an offence for the journalist not to answer questions or hand over materials, with no protection for confidential sources.

Rebecca Vincent, the UK bureau director for Reporters Without Borders, said “This bill has extremely worrying implications for press freedom and the protection of journalistic sources.

“We have underscored our concerns over a number of specific clauses that should be struck, or at a very minimum, amended to include clear exemptions for journalistic activities. We call on lords to carefully scrutinise this problematic bill and amend it to ensure that it does not contribute to further deterioration of UK press freedom.”

A Guardian News & Media spokesperson said: “The counter-terrorism bill poses a serious threat to press freedom, as it would potentially criminalise legitimate journalism and put at risk confidential sources and materials.”

Elsewhere, the campaigners said that plans in the bill to criminalise expressing an opinion that is “supportive” of a banned group if the person does so in a way that is “reckless” comes to close too “making opinion a crime”.

They also flag that proposals to make it a crime to view online content that is likely to be useful for terrorism, even if you have no terrorist intent, would make the work of investigative journalists and academic researchers difficult or impossible.

Other signatories backing the statement include the Committee on the Administration of Justice, Liberty, Article 19, the National Union of Students, Big Brother Watch, Rights Watch (UK) and Open Rights Group. The House of Lords will consider the bill at committee stage on 29 October.

The home secretary, Sajid Javid, previously defended the proposed anti-terror laws in an article for the Guardian, insisting they were “not part of a sinister strategy to create an Orwellian state”, adding: “I totally reject any attempt to simplify today’s debate into one of security versus liberty.”

On Wednesday night, a Home Office spokesperson said: “It is our view that the measures in the counter-terrorism and border security bill are necessary, proportionate and compatible with the European convention on human rights.

“After the spate of terrorist attacks of last year and the deadly nerve agent attack in Salisbury, our intelligence services and police made the case for an update of existing legislation and some new powers to help meet their operational needs and respond to the evolving threats posed by terrorism and hostile state activity.”