The Daily Express has repeatedly warned its readers that “militant trade unions” are bringing Britain to its knees – but this week many of the newspaper’s own staff will go on strike in protest at the outlet’s low pay.

They will join journalists at sister outlets including the Daily Mirror, the Daily Star and dozens of local newspapers in striking on Friday. It marks the start of a month of industrial action designed to disrupt production at the news outlets, which are all owned by publishing giant Reach.

Although one journalist at the titles acknowledged that a rightwing anti-union newspaper going on strike is a “satirist’s dream”, they insisted there is solidarity between unionised staff across all of Reach’s titles, regardless of their political stance. Members of the National Union of Journalists voted to go on strike after rejecting bosses’ offer of a 3% pay rise as not enough to cope with the cost of living crisis.

While Reach chief executive Jim Mullen took home £4m last year, many of his journalists say they are struggling financially. Starting salaries for reporters on Reach’s national newspapers are about £22,000 – well below the median average British salary for jobs that often require extensive training and experience. Regional newspaper journalists can earn under £20,000, with many now facing increased energy bills due to a permanent shift to home working. One issue facing striking staff on Reach’s local newspapers is that it is unclear how they can picket their workplace, given that Reach has closed most of its local newspaper offices.

Matt Capon, an organiser for the Mirror branch of the NUJ, said: “Our members are focused and clear on what they want – a dialogue with the company to make them understand that the cost of living is an issue that affects everyone, including journalists.”

Reach – formerly known as Trinity Mirror – is one of the biggest employers of journalists in the UK. In recent years it has bought up dozens of newspapers including the Daily Express and Daily Star in addition to launching new local web-only sites under the “Live” branding.

In an attempt to limit the extent of the action, bosses have written to staff reminding them that anyone who strikes will give up their right to take part in an annual share bonus scheme. Staff have also been asked to contact the company if they feel pressured into striking.

Journalists at the Mirror are particularly aggrieved by the juxtaposition between the outlet’s stated leftwing political beliefs and its treatment of employees. The newspaper has repeatedly criticised the fat-cat pay of executives and inequality in society.

There is a still chance that talks on pay could resume, amid speculation that Reach will make a last-minute financial offer in a bid to win over staff. Some Mirror journalists represented by the rival British Association of Journalists union have already voted to accept the 3% pay deal in the belief the company will not go any higher.

Despite its rightwing political stances in recent decades, staff at the Express have a strong history of union activity. The NUJ general secretary, Michelle Stanistreet, worked for the Express before becoming a full-time union official. Even the newspaper’s bosses do not necessarily come from a rightwing tradition; the Daily Express’s editor, Gary Jones, is a lifelong Labour voter.