The Aam Aadmi Party leader said Delhi residents were "still reeling" under the impact of the previous "steep fare hike" in May and said the proposed hike from October 10 "will be simply unacceptable in this time of economic distress".
Kejriwal said while the Fare Fixation Committee (FFC) had recommended a gap of one year between two fare hikes, the DMRC was going ahead with it in less than six months.
He said that put together, the two hikes accounted for over 80 per cent increase in one year alone even as the FFC recommended that from 2019 onwards, the annual hike should not exceed seven per cent.
"There is no reason why the principles to be followed from 2019 onwards should be completely violated in 2017," Kejriwal wrote in his letter.
However, the DMRC justified its decision by citing increased input costs and that the increase was at par with those in other city Metro rails.
"A comparison of Metro fares in other cities in India shows DMRC's maximum fare is either less or comparable to others despite higher per capita income in Delhi," the statement said.
"Since 2009, there has been no fare increase whereas input cost for the DMRC has increased by over 105 per cent in energy, 139 per cent in staff cost and 213 per cent in repair and maintenance," a DMRC statement said.
"In addition, the DMRC has taken a huge loan from the Japan International Cooperation Agency and a payment of Rs 26,760 crore is still to be paid back," it said.
It also said that once Metro's third phase gets operational, commuters will have to travel shorter distances and hence pay lesser.
The DMRC said a long gap of over eight years in FFC formation led to fare hike in steps, which if seen on yearly basis "is in the reasonable range of seven to eight per cent per annum", taking into account both the phases of the hike.
The statement said despite efficient operations, the DMRC was suffering a net loss of Rs 378 crore.
"In order to continue providing world-class service, it is essential to operate as a healthy organisation," the corporation said.
Delhi Metro has been operating in the national capital since 2002, and carries around 27 lakh passengers every day.
While Kejriwal said in his letter that no DMRC initiatives were visible to improve efficiency so as to reduce costs, the Delhi Metro said it was constantly making efforts to reduce its operating cost by going for solar power projects and increasing energy efficiency at its stations, besides introducing new initiatives on property development and property business fronts.
"The DMRC is consistently increasing the number of trains, AFC gates, lifts, escalators, and other passenger services, leading to increased input cost but are nevertheless essential for providing world-class service," the Metro statement said.