Coal India Ltd's output could be affected by a planned strike on Wednesday, a senior official at the state-run company told Reuters.

Worker unions affiliated to left wing groups and political parties have called a strike across India on Wednesday to protest over Prime Minister Narendra Modi's government's policies which they say have hurt the working class.

"Production could be adversely affected at some subsidiaries," the senior company official said.

Coal India's December production rose after five straight months of declines, the latter reflecting the heaviest monsoon rains in 25 years, strikes and protests.

Gouranga Chatterjee, organising secretary of the coal workers unions, said production at Coal India would be affected as the striking unions have a sizeable following.

The Bharatiya Mazdoor Sangh, affiliated to Modi's party, is not participating in the strike