RAIL union chief Mick Lynch has criticised "anti-democratic" plans by Westminster to weaken workers' rights in Wales.
Lynch, head of the railworkers' union RMT, told The National Wales that his members would use "all legal means and peaceful civil disobedience" to resist the UK Government's efforts to curtail strike action.
Those efforts include overturning a Welsh law passed in 2017 that bans the use of agency staff when public sector workers go on strike - a move which prompted Plaid Cymru leader Adam Price to call for a referendum on Wales's future in the United Kingdom.
The announcement by Westminster is thought to be a reaction to last week's RMT rail strikes, which saw around 50,000 railway staff across the UK - from ticket collectors and cleaners to signallers - walk out over pay cuts and working conditions.
Teachers, doctors, firefighters and postal workers are just some of those that could join RMT in striking over the coming weeks and months - again over pay cuts, jobs and working conditions - and bringing in agency staff would damage the ability of these workers to win their disputes.
"This latest attack on trade union rights is not just an attack on all trade unionists, but an anti-democratic move to undermine Welsh devolution," said Mick Lynch.
“Using agency workers to break strike action is immoral, impractical and unsafe on the railways - our members are highly skilled and cannot simply be replaced by agency staff.
“RMT will use all legal means and peaceful civil disobedience to resist any further attacks against trade union rights.”
His words echo those of First Minister Mark Drakeford this week, who called the idea of using agency staff to cover striking railworkers "a piece of nonsense", and blasted Westminster's "disrespectful agenda" towards Welsh democracy and devolution.
In Scotland, First Minister Nicola Sturgeon also hit out at the proposals to bring in agency staff to replace striking workers - as a Scottish Government spokesperson said the Holyrood government hadn't been told about the plan.
Unions in Wales say they are now working with the Welsh Government to consider their strategy going forward.
"We are fundamentally opposed to this power grab," said Tom Hoyles, political officer at the union GMB Wales, which represents public and private sector workers from a range of industries.
"We wholeheartedly welcome Mark Drakeford's words yesterday and the leadership he has shown on this.
"This move from the Tory UK government tramples all over the devolution settlement and is a direct threat to our members' democratic right to protest against employers.
"GMB will pull every lever we have, and right now we are working on our strategy with our partners in sister unions, Wales TUC [Trades Union Congress] and the Welsh Government."
A spokesperson from the PCS union in Wales - which represents employees of UK Government agencies like the HMRC - also said the UK Government's plans wouldn't work.
Its members at the DVLA headquarters in Swansea staged a series of strikes last year over safety and working conditions.
The spokesperson said: "The government should stop picking fights with trade unions and instead resolve the causes of the disputes – the cost-of-living crisis, below-inflation pay increases and a heavier workload with fewer resources.
“Bringing in agency workers won’t resolve any disputes.
"That can only be done by reaching a negotiated settlement with unions, so why is the government not doing that?”
