Blood testing staff in Leeds and Bradford are striking for 24 hours over new working patterns they say will put patients and staff at risk.
Around 140 employees are taking action at St James, Leeds General Infirmary and Bradford Royal Infirmary.
The staff, who test blood and monitor transfusions, claim salaries could be cut.
The trust say contingency plans are in place and emergency services are unaffected. We spoke to Carole McBride who is works in blood transfusion.