The women, who worked at Kinsley Academy, claimed their pay had been cut after the contract switched from Wakefield Council to C&D Cleaning.
The three women were reportedly dismissed by C&D Cleaning on Monday.
C&D have been approached for comment but confirmed to the Guardian the trio had had their employment terminated.
Labour MP for Hemsworth Jon Trickett said: "With only days till Christmas it looks like Scrooge has been brought back to life from Victorian times."
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Lesley Leake, Karen McGee and Marice Hall went on strike in September saying their pay had been slashed and their pensions, holiday and sick pay had also been cut when the contract changed hands after the primary school became an academy.
In October about 100 people joined the women on a protest march through Barnsley, where C&D Cleaning is based.
According to reports the women were sacked following a disciplinary hearing on 19 December.
Labour Leader Jeremy Corbyn said: "I am angered that three striking primary school cleaners from Kinsley have been sacked.
"When I met them, they explained how their wages were cut following the outsourcing of their contracts to a private company.
"Outsourcing is bad for our public services and workers. The cleaners' jobs must be brought back in-house with fair pay and conditions."
The BBC has approached C&D Cleaning for a comment.
In a statement published in the Guardian, the company said the women had been invited to a disciplinary hearing to "respond to allegations of gross misconduct".
It said: "The outcome of the hearing was termination of employment.
"The company will not comment further at this stage so as not prejudice any internal process."
Unison general secretary Dave Prentis said: "These women bravely took action to protect their wages and employment rights.
"To then sack them just days before Christmas is heartless in the extreme."

Statues are smashed using sledgehammers and drills in what seems to be a museum in the city of Mosul.
Statues are also shown being destroyed at an archaeological site known as the Nergal Gate.
World heritage body Unesco has called for an emergency meeting of the UN Security Council to discuss how to protect Iraq's cultural heritage.
In a statement, Unesco head Irina Bokova said: "This attack is far more than a cultural tragedy. This is also a security issue as it fuels sectarianism, violent extremism and conflict in Iraq."
In the video released via IS social media sites, black-clad men push over statues, smash them with sledgehammers and use a pneumatic drill to destroy the rubble.
The video shows a black-clad man drilling through and pulling apart what appears to be a stone winged-bull Assyrian protective deity that dates back to the 9th Century BC.
One of the militants in the video describes the artefacts as "false idols" and seeks to justify their destruction in religious terms.
Analysts say the artefacts are unique and priceless although the museum does also house copies of some items.
Ihsan Fethi, an Iraqi professor of architecture based in Amman, Jordan, told Agence France-Presse the destruction was "a terrible loss and an unbelievable act of cultural terrorism".
Amir al-Jumaili, a professor at the Archaeology College in Mosul, told Associated Press: "I'm totally shocked. It's a catastrophe. With the destruction of these artefacts, we can no longer be proud of Mosul's civilisation."
IS have controlled Mosul, Iraq's second largest city, since June 2014. The US military have said that an assault on the city by the Iraqi army could happen within months.
The region under IS control in Iraq has nearly 1,800 of Iraq's 12,000 registered archaeological sites.
The reported destruction of the statues follows recent reports that IS burnt down Mosul Library, which housed over 8,000 ancient manuscripts.
Three cleaners who went on strike over a pay dispute have been sacked in a move branded Scrooge-like by one MP.
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The Islamic State (IS) group has released a video appearing to show the destruction of statues in Iraq.