"The alliance has taken place at the lower level and it is a fact. The workers have come together to unitedly fight the atrocities and terror unleashed by the ruling party," Chowdhury, a known detractor of state Chief Minister Mamata Banerjee, told reporters at the AICC briefing.
Asked what was the view of Congress high command on the alliance, he said "our leadership is not blind. It is very conscious. Our views are very clear. In order to defeat (ruling Trinamool Congress) all democratic and secular forces should come together."
State units of Congress and also CPI(M) have pitched for an alliance.
Congress had contested the last Assembly polls in alliance with Trinamool Congress which led to the ouster of CPI(M)-led Left Front from power after over three decades of rule.
Chowdhury, who was Minister of State for Railways, dismissed the NDA government claims that the provisions in the railway budget 2016-17 would help development of eastern India including West Bengal.