He alleged officials have been leaking Election Commission's "predetermined intention" to return his petition as outside the scope of its powers under Constitution.
Swamy had on Saturday moved the Election Commission seeking derecognition of Congress, alleging the party violated laws by providing a Rs 90 crore loan to a company that published the now-defunct National Herald newspaper.
In the letter to Chief Election Commissioner V S Sampath, he said the "leaks raise a serious question on the impartiality of the Election Commission and whether the EC is acting in an arbitrary and unreasonable manner".
He said such leaks were "tantamount to a predetermined decision" even before the hearing is held, and which is "favourable" to the ruling party.
"Kindly put a stop to these leaks as it violates my rights...In my dealings with the Election Commission for getting justice and fair hearing," Swamy said.
