Falana said said the National Security Agencies Act limits the DSS to investigate crimes against the internal security of Nigeria.
According to reports, the security agency stormed the Green Chambers and locked the secretariat of the appropriation committee.
The lawyer’s stand was also expressed by the House minority leader, Leo Ogor, in an interview with Premium Times.
Falana also said the DSS lacks the moral and legal right to probe the budget padding scandal in the House of Reps.
He said the National Security Agencies Act limits the DSS to investigate crimes against the internal security of Nigeria.
Falana, in a statement said: "It was reported last week that the Nigeria Police Force had commenced investigations into the criminal allegation of the padding of the national budget by some members of the House of Representatives.
“Some civil society organisations have also requested the Economic and Financial Crimes Commission and the Independent Corrupt Practices and Other Offences Commission to wade into the matter. Curiously, the State Security Service (Department of State Service) is alleged to have usurped the statutory duties of the police and the anti graft agencies by taking over the investigation of the padding of the budget.
“Based on the illegal decision to take over the investigation the DSS is reported to have sealed off the office of the Chairman of the Appropriation Committee of the House of Representatives.
“Having regard to the recent activities of the SSS and the clear provisions of the relevant laws on investigation of corruption and other economic and financial crimes the DSS lacks the moral right and legal powers to interfere in the investigation of the criminal allegation of padding of the budget in any manner whatsoever.
“More importantly, by virtue of the provisions of the National Security Agencies Act the powers of the SSS are strictly limited to the ‘preservation and detection within Nigeria of any crime against the internal security of Nigeria.’
“Since the padding of the national budget is a straight forward case of economic crime which is not concerned with the internal security of the nation the SSS should not play into the soiled hands of the criminal suspects in the House of Representatives as they may later turn round to challenge the legal validity of any criminal charge arising from a faulty investigation report.
“The SSS should be called to order as the nation cannot afford to bungle the investigation of the highly placed politically exposed persons involved in the padding of the budget.
“In the light of the foregoing, the Police and the anti graft agencies should be allowed to get to the root of the criminality of budget padding in the National Assembly.”
There are reports that President Buhari gave the DSS and police the go ahead to investigate the budget padding scandal.
Abdulmumin Jibrin, the former chairman of the House of Representatives committee in appropriation, has called on the Economic and Financial Crimes Commission (EFCC) to arrest Yakubu Dogara.