Hundreds of Scottish Water workers are to walk out on Friday in what marks the first day of a four-day strike following a pay and grading dispute.
It comes after First Minister Humza Yousaf said he hoped the strikes could have been averted.
The union Unite, which represents striking Scottish Water workers, branded talks a “waste of time”.
Sharon Graham of Unite previously said Scottish Water “failed to address the concerns of our members”.
She said the firm has “continued to press ahead with its proposed new grading structure” for staff, adding this is “foolishly” being linked to pay.
“Talks have been a waste of time,” Ms Graham said.
“It appears to be the case that the bosses in the boardroom will only listen to us when our members have taken to the picket lines across Scotland.
“Unite will fully support our members in the fight for better jobs, pay and conditions at Scottish Water.”
Some 500 workers from the Unite, Unison and GMB trade unions are set to commence strike action as part of the row.
Action is planned to run for 48 days over a three-month period, with the first walkout due to last four days.
Unison regional organiser Emma Phillips previously said: “Scottish Water truly are a rogue employer.
Strike action is always a last resort but Scottish Water managers are imposing a new pay structure with no involvement from staff, which is not acceptable— Patricia McArthur, Unison
“Our strong ballot result shows the strength of feeling among our members, who have overwhelmingly rejected the employer’s slapdash proposals.
“Despite this, Scottish Water are insisting they are still going to implement the changes to employment contracts and pay structures.”
Patricia McArthur, the union’s branch secretary at Scottish Water, said: “Strike action is always a last resort but Scottish Water managers are imposing a new pay structure with no involvement from staff, which is not acceptable.”
GMB Scotland organiser Claire Greer said: “It is impossible to underestimate how ineptly the company has handled what should have been a straightforward negotiation.
“It has managed to infuriate a committed workforce and drive them to strike action, when the dispute could have easily been resolved months ago.
“Scottish Water has repeatedly been given a clear choice between doing the right thing and making the situation worse, and has taken the wrong decision every single time.
“Its actions over the last six months are a template for how to demoralise staff and demolish industrial relations.
“The priority is to resolve this dispute, but then lessons must be learned.”
Mr Yousaf, meanwhile, defended bonus payments made to Scottish Water executives.
He had been challenged on the payments by Labour MSP Pauline McNeill, who raised reports that three senior staff members had received almost £1.1 million in bonuses in 2021, claiming this was “in excess of public sector pay rules”.
She told the First Minister the “same executives are withholding a pay rise from their workers unless the staff accept a new pay structure”.
Mr Yousaf told her the bonuses were “in line with public sector pay rules” and help Scottish Water “attract and retain highly experienced personnel to run a vital public service”.
Regarding workers’ pay, he said the Scottish Government “has a very strong track record of ensuring workers are paid fairly”.
Scottish Water was previously contacted for comment.
