Fearing rejection of nomination, Brigadier Khushal Thakur (Retired), a decorated officer who played a crucial in the 1999 Kargil war, on Friday filed nomination papers as the substitute candidate for BJP's Ram Swaroop Sharma for Mandi seat in Himachal Pradesh.
Mr Sharma's candidature was challenged in the election office by the state opposition Congress.
A substitute or a covering candidate is fielded by every political party as a backup in case the candidature of the main nominee is rejected after scrutiny.
Mr Sharma, 60, the outgoing BJP Lok Sabha lawmaker, on April 24 filed his nomination papers for a second term.
"I am told by the party three-four days back to file the nomination papers. Since the process to file the nomination takes time, so I filed it today," Mr Thakur, who defended the borders as Commanding Officer of 18 Grenadiers in Indian Army, told IANS.
The Congress has moved the Election Commission regarding Mr Swaroop's failure to file his income tax returns for four years from 2014-15.
Congress state unit President Kuldeep Rathore said it was surprising that the Income Tax Department had accepted Mr Swaroop's request for condoning delay in filing of income tax returns.
He said the reason cited by the lawmaker in his application that he could not file his returns due to his engagements as a public servant was highly irresponsible.