Three long-serving primary school cleaners, who went on strike over claims their wages and conditions were cut when a private company took over the contract, have been sacked days before Christmas.

The women – Lesley Leake, Marice Hall and Karen McGee – sparked a debate over outsourcing when they went on strike for 14 weeks after their school in West Yorkshire was turned into an academy earlier this year.

Known as the “Kinsley cleaners”, the women said they had their wages cut from £7.85 an hour to the minimum wage of £7.20 once the contract switched from Wakefield council to C&D Cleaning in April.

The women, who between them have more than 28 years’ experience cleaning Kinsley primary school, returned to work earlier this month. But on Thursday they were told they had been sacked.

Jeremy Corbyn said he was angered by the news of the cleaners’ dismissal. “When I met them, they explained how their wages were cut following the outsourcing of their contracts to a private company,” the Labour leader said.

“Outsourcing is bad for our public services and workers. The cleaners’ jobs must be brought back in-house with fair pay and conditions. The race to the bottom in wages and working conditions faced by huge numbers of workers right across Britain is a national disgrace and Labour would put a stop to it.”

Dave Prentis, the Unison general secretary, said the women had bravely taken action to protect their wages and employment rights. “To then sack them just days before Christmas is heartless in the extreme,” he said, adding that the union would be consulting lawyers over the decision to dismiss them.

Speaking to the Guardian in October, Leake – who has two adult children and a second job – said her pension, sick pay and holiday entitlement had also been hit by the outsourcing. “The first month [under C&D Cleaning] when we got our payslips we just thought it could be a few teething problems, but the second month it was the same, and it just went on and on,” she said.

The women said they had tried to raise the issues with C&D Cleaning but were “fobbed off”. In the end the three got in touch with their union, Unison, but C&D Cleaning, based in nearby Barnsley, was reluctant to discuss the women’s cases.

In one email seen by the Guardian, the company’s head of human resources, Nick Thorpe, replied to Unison: “I understand … the impact for you as an organisation when members realise that we are no longer living in the 1980s and they question the actual value of union membership when you have no say, power or influence over their employer.”

The three women decided to go on strike, staging their first picket outside the school at the beginning of September. “It was a bit scary at first because none of us have ever done anything like this, but we didn’t know what else we could do,” said Leake. “It wasn’t just the money we were losing, it was the stress that was affecting us and our families as well.”

A statement from C&D Cleaning read: “The employees were invited to a disciplinary hearing on an earlier date in December to respond to allegations of gross misconduct. At the employees’ request, the hearing took place on 19 December 2016 as their chosen Unison representative was not available on the earlier date.

“Full details of the allegations were provided to the employees in advance of the hearing. The employees and their representative were given full opportunity to put their cases. The outcome of the hearing was termination of employment. The individuals have been informed of their right of appeal. The company will not comment further at this stage so as not prejudice any internal process.”

Jon Trickett, the local MP, said all the “three courageous women” had done was stand up for their right to work. “With only days until Christmas, it looks like Scrooge has been brought back to life from Victorian times and ruined the festive period for three families in my constituency,” he said.

He said the women’s experiences were unfortunately common. “Our country needs better pay, better conditions and better corporate governance to make sure that all employees are treated fairly,” he said. “It is also time that we stopped outsourcing services paid for by the taxpayer to rogue employers.”