Gamlin took charge of the post hours after Kejriwal sent her a letter asking her not to do so as her appointment was "against" the rules.
Jung had on Friday appointed Gamlin as Delhi chief secretary, notwithstanding strong opposition to her nomination by Kejriwal dispensation which alleged that she had close links with BSES discoms. The 1984-batch officer has, however, denied the charges saying they were baseless.
Chief Secretary K K Sharma has left for the US on a personal visit due to which the government had to appoint an acting chief secretary. Gamlin is currently serving as power secretary.
"The BJP through LG of Delhi has attempted a coup against the democratically elected government of Delhi with highest ever mandate in the history of the state.
"This is for the first time that LG is issuing direct instruction to officers, bypassing the chief ministers and council of ministers," Manish Sisodia, who also holds charge of Services department, told PTI.
Meanwhile, Parimal Rai, who was backed by Arvind Kejriwal, declined to become acting chief secretary, noting that he respects the Lt Governor's directions. The Lt Governor on Friday gave the additional charge of chief secretary to Gamlin, hours after she wrote a scathing letter to Jung claiming that she was pressured by a senior bureaucrat in CM's office to withdraw from the race.
"The Constitution, GNCT act of Delhi and Transaction of Business Rules clearly define what LG can do. In case of a dispute or difference of opinion between LG and council of ministers, LG could have called the minister concerned to discuss the matter," Sisodia said.
Jung had rebutted AAP government's allegations saying under Article 239 AA of the Constitution of India, the the Lt Governor is the representative of State Authority in Delhi.
"Even after that if council of ministers disagreed, he could have referred the matter to the President and his advice could have been conveyed to council of ministers," the deputy chief minister said.
Calling LG's move an act "against the Constitution", Sisodia said, "I was not informed by LG and he does not have power to issue direct instructions to officers. He has clearly acted against the Constitution and laws relevant to Delhi."