Unite general secretary Sharon Graham has pledged to challenge changes to Taylor Wimpey construction workers' contracts in the North East.
The union says 31 joiners and 19 scaffolders have received dismissal notices as part of proposals to reduce bonus payments and re-engage them on inferior terms.
Graham criticised the move and said Unite was considering industrial, legal and political options to protect members.
The dispute has also reached Parliament, where Labour MP Ian Lavery urged the company to withdraw the notices and resume meaningful negotiations.
Taylor Wimpey says a regular benchmarking exercise identified a small number of direct-labour roles whose terms required review. It says no final resolution has been reached and talks are continuing.
The union's allegations and the company's explanation concern an ongoing dispute, rather than a concluded legal finding.
