The UK government on Tuesday introduced proposals to make "minimum safety levels" compulsory during strikes, prompting angry unions to accuse ministers of "criminalising" industrial action and threaten legal challenges.

The new law will require minimum levels of service during walkouts by various workers, including healthcare staff, firefighters and railway employees, "to ensure that vital public services will have to maintain a basic function".

It follows months of disruptive stoppages across the private and public sectors, as decades-high inflation fuels the worst cost-of-living crisis in a generation and demands for hefty pay rises.

"We do not want to use this legislation, but we must ensure the safety of the British public," Business Secretary Grant Shapps told MPs as he introduced the bill in parliament.

He said the government would consult "on what an adequate level of coverage looks like" for emergency responders and rail workers.

Meanwhile ministers would bid to strike agreements on levels in other sectors covered by the bill, including health, education, border security and nuclear decommissioning.

"This is a common-sense approach and we're not the first to follow it," he added, noting European neighbours had similar rules.

But unions locked in pay disputes with the government and employers savaged the plan, arguing that it undermines the right to strike.

"The government should be putting money in our members' pockets, not trying to put our members behind bars," Mark Serwotka, head of the PCS union representing civil servants and others involved in recent walkouts.

"Criminalising the people who keep our borders safe is not the way to resolve an industrial dispute," he added, referring to striking Border Force staff.

"It's reprehensible, provocative and vindictive, and we'll fight the legislation every step of the way."

Other unions echoed the criticism, with TUC general secretary Paul Nowak calling the plans "undemocratic, unworkable, and almost certainly illegal".

- 'Disappointing' -
 

The main opposition Labour party, which is part-funded by 11 trade unions, has said it will repeal any such legislation that makes it onto the statute books ahead of the next general election, due within two years.

Its deputy leader Angela Rayner, a former senior official for the Unison trade union, accused the government of "playing politics with nurses' and teachers' lives".

Addressing lawmakers after Shapps, she added: "We need negotiation not legislation."

Conservative party Prime Minister Rishi Sunak -- who only took power 11 weeks ago -- has insisted recession-hit Britain cannot afford to reopen public sector pay already set for this fiscal year, which ends on March 31.

He has hinted at the possibility of more flexibility in agreeing upcoming salary deals, handled by pay review bodies whose independence from government has been questioned.

But unions are unwilling to accept that and the ensuing standoff with various sectors, from health to the civil service to the railways, has led to months of crippling strikes.

Five days of walkouts last week on the rail network, which is largely run by private firms but under condition-heavy government contracts limiting their autonomy, left city centres deserted compared to normal weekdays.

Businesses and economists have pointed to the heavy fallout for the country's struggling economy.

Meanwhile industrial action by nurses -- the first in their union's 106-year history -- and paramedics has stretched the already severely strained National Health Service (NHS).

Ambulance workers in England and Wales will walk out again on Wednesday while nurses will follow suit again next week.

Talks Monday between unions and government ministers appeared to make little headway, with a nurses' union leader branding their meeting "bitterly disappointing".