"Illegal phone tapping is unjustified but in this case, it is for the government to explain whether phone tapping was done or not or whether it was legal or not," party spokesperson Shakeel Ahmed said.
The Congress leader's remark comes in the wake of reports in a weekly magazine alleging that government agencies have been tapping phones of important politicians and ministers since 2006.
Reacting to it, main Opposition Bharatiya Janata Party has said it will raise the issue in Parliament.
"If the government is tapping the phones of terrorists, or tax evaders or secessionists, then it is understandable as national interest and national security are involved. But tapping phones of politicians and ministers is condemnable," BJP deputy leader in Rajya Sabha S S Ahluwalia said.
Ahluwalia insisted that this was violation of Article 21 of the Constitution which assures protection of life and personal liberty of every citizen.
Communist Party of India - Marxist general secretary Prakash Karat termed as 'illegal and intolerable' the reported tapping of phones of political leaders and asked the government to take action against those responsible for the acts.
"The United Progressive Alliance government is resorting to tapping of phones of political leaders which is illegal and intolerable. The government has to own up responsibility and take action against those responsible," said Karat.
He said further safeguards should be taken against such misuse of security agencies. His comments came in the backdrop of a magazine report that phones of prominent political leaders including Union Agriculture Minister Sharad Pawar, Congress leader Digvijay Singh and Karat have been tapped.
The phones of Bihar Chief Minister Nitish Kumar have also been tapped by the National Technical Research Organisation, an intelligence agency created in the aftermath of the Kargil war to cover all aspects of technical intelligence gathering, Outlook magazine claimed in its latest issue.
While the phones of Singh and Kumar were tapped in 2007, Karat's phone was tapped in 2008, at the height of his opposition to the Indo-United States nuclear deal, leading to the no-confidence motion against the government. Pawar's phone was tapped last fortnight in the wake of the IPL scandal.