The legality behind the extension of tenures for CBI, ED directors

How have the existing Rules/Acts been amended to facilitate this?

The Union Government has brought in two ordinances allowing the service of the directors of the Enforcement Directorate (ED) and the Central Bureau of Investigation (CBI) to be extended beyond their fixed tenure of at least two years up to a maximum of five years. The extension can be given only one year at a time. That is, after a fixed two-year tenure, they may get three annual extensions. The current ED chief, Sanjay Kumar Mishra, whose term was to have ended on November 17, is the first officer to have received a one-year extension under the new rule.

The Government's move has drawn sharp criticism from the Opposition parties, which have accused it of taking the ordinance route despite the Parliament session beginning on November 29. At least three petitions have been filed in the Supreme Court, challenging the validity of the ordinances.