“We find ourselves deeper into the labour dispute,” said Verdi spokesperson Andreas Splanemann.
The BVG suggested commuters who normally ride trams instead use the city's buses and subways. However, the streetcars are a key part of the public transportation network in eastern Berlin.
Verdi had threatened new strikes on Wednesday, and Splanemann said he was unsure if the union would agree to a no-strike clause because talks with BVG employers may not continue.
The union has asked for a 9 percent wage increase for the some 12,000 BVG workers who man Berlin's extensive transport system.
BVG offered a total of €24 million for two years, an amount that Verdi said is inadequate to inflation.
During the 12-day March strike, BVG bus, subway, and tram drivers left their vehicles standing, leaving the elevated S-Bahn trains, run by Deutsche Bahn, as the only public transportation in service.
Verdi ended the March strike in consideration of passengers, even though they failed to reach a solution to the wage dispute in ongoing negotiations.