The union said the legal action was “a massive waste of taxpayers’ money”.
It added the only way to solve the dispute was for the authority to get back into negotiations and “put forward a reasonable offer”.
The council said it would continue to call for Unite members to end the strikes.
It also said it was continuing to consider legal options, including whether to appeal against the decision.
The council has also set up two additional drop-off points for household waste.
The sites, at Victoria Park and Alder Lane in Orford, will be open on weekdays between 10:00 and 16:00 GMT.
The new action has started a day after the previous strike, which began on 21 November, ended.
Before that, staff walked out from 3 to 16 October, 24 October to 6 November and 8 to 20 November.
