Two different groups of London Underground workers are to be balloted for strikes in separate disputes over jobs, pay and conditions.
The RMT union said scores of control centre and maintenance staff will be urged to back industrial action.
Some of the workers are employed by a contractor, which the union said had rejected a claim for an Olympic bonus payment.
Pageant spectators complained at the level of service provided by major rail companies. Many of them took to Twitter to vent their anger.
Londoners are being warned that central London will be extremely busy throughout the Diamond Jubilee weekend.