The strike started at 7 a.m. Tuesday at seven donor centers in Philadelphia and Willow Grove in Pennsylvania along with Pennsauken and Princeton in New Jersey.
Members of Health Professionals and Allied Employees Local 5103 say the two sides can't agree on issues including collective bargaining rights, staffing and scheduling.
"Our issues are about staffing, scheduling and making sure staff have proper time to make sure donors are properly screened and blood supply safe," said HPAE spokesperson Jeanne Oterson.
"We screen you to make sure the blood is safe, that you haven't done anything or gone anywhere that's going to put it at risk," said striking nurse Judy Merkowsky.
The union maintains the Red Cross is putting too many donors on schedule with not enough staff in an attempt to maximize profits, saying the blood services division these people work for is a $2 billion industry.
"It's a national cost-cutting move by an organization that has a humanitarian image, but it's not how they treat the people who work for them," said Oterson.
Red Cross Spokesman Anthony Tornetta says they average between 25 and 30 blood drives each weekday and that this strike has led to schedule modifications.
Tornetta went on to say the strike will likely have little effect on the short-term blood supply and that the Red Cross is able to bring in blood from other regions if need be.
"We have the ability to maintain a stable blood supply to hospitals and patients need not worry. There will be blood on shelves when it's needed," said Tornetta.
Tornetta said people can still donate blood but should check with the Red Cross for any scheduling changes.
Call 1-800-RED-CROSS.
