The government’s plans to give employers powers to force striking workers back to work is akin to modern slavery, legal experts told MPs.

Last month, business secretary Grant Shapps unveiled plans that would require unions to maintain “minimum service levels” in fire and rescue, transport, health and education sectors during strikes.

The bill proposes to allow employers to issue so-called work notices to a proportion of striking workers that require them to return to work. Workers that do not comply with the notices would lose their protections from unfair dismissal.

Legal scholars warned the cross-party MPs on the Joint Committee on Human Rights on Wednesday that the measure could breach Article Four of the Human Rights Act, which prohibits forced labour.

“Forced labour, as it is defined by the European Court of Human Rights, involves a situation where somebody is required to work under the menace of a penalty. And here the menace of the penalty is potentially dismissal,” said Tonia Novitz, a professor of labour law at the University of Bristol Law School.

“Although Article Four does make an exception for services exacted in case of emergency or calamity, threatening the life or wellbeing of the community, this bill goes well beyond that. And the threat of dismissal is really stark in the context of a cost of living crisis. So yes, I think there is a real analogy to be drawn here with modern slavery.”

Other witnesses told the committee that the bill would effectively require unions to break their own strikes.

“There’s not a duty on the part of the union not to obstruct – or to refrain from obstructing – the operation of the work notice. [But rather] it’s a duty to ensure that members comply. That is a very, very strong obligation of a very vague and uncertain nature to be included in a bill of this kind,” said Tim Sharp, a senior employment rights officer at the Trades Union Congress.

“It seems to me that that alone gives rise to serious freedom of association questions. It’s imposing a duty on the union to cooperate with the employer to ensure that the strike is defeated, which is an extraordinary thing for Parliament even to contemplate.”

Under the proposal, unions could be sued by employers for damages of up to £1m if they failed to take “reasonable steps” to ensure their members comply with work notices.

The government has sought to justify the bill by drawing comparisons to similar laws already in place in some European countries including France and Germany.

But witnesses dismissed the comparison and told MPs that only Hungary has implemented measures like the UK is proposing.

“Hungary is at the moment subject to a European Parliament resolution that it is no longer a full democracy,” said Novitz. “It is a state where, since December 2010, quite draconian legislation has been introduced in respect of minimum service levels.

“And in 2022, the International Labour Organisation committee of experts has said that it is problematic legislation. Why is it problematic? Because there is no way for the workers’ organisations to participate in establishing the minimum service level, together with employers and public authorities.”

European trade unions have also previously rubbished the comparison, pointing out that minimum service levels are negotiated with unions in other countries and workers cannot be forced to return to work.