Docklands Light Railway (DLR) workers are to strike in a dispute over a planned change to working patterns.
Workers will strike on July 3
The Rail, Maritime and Transport (RMT) union said 250 members will walk out on 3 July in protest at plans they say compromise safety and will reduce pay.
The RMT said lower paid staff will "displace experienced safety-critical platform staff".
Docklands Serco, which runs DLR, said it was increasing station staff because passengers wanted to feel more secure.
Serco managing director Tony Thomas also said there would be "absolutely no compromise to safety".
"The new proposal means there is no loss of pay, no downgrading and no redundancies for existing station staff."
He said that the only change for existing staff would be an increase in the time on trains and a decrease in the time on stations.
Fifteen new staff will be recruited to work only on stations.
The union claimed Serco wants to cut station staff from 42 to 34 and reduce station assistants' pay by £5,000.
Mr Crow said: "It is scandalous that a rail franchisee should even try to reduce properly-trained staff in an industry that needs more and better safety and security."
The RMT also claims the company wants to sack or downgrade more than half of the current station supervisors.