There are two kinds of privileges that every member of the Congress enjoys, to wit: immunity from arrest and privilege of speech and debate.
Immunity from arrest.
Intended to ensure representation of the constituents of the members of the Congress by preventing attempts to keep him from attending its sessions, they shall not be arrested, while the Congress is in session, for offenses that are punishable by not more than six years. Session herein refers to the entire period from its initial convening until its final adjournment, eg. July 27 to October 16. Thus, freedom from arrest can be enjoyed even though the member is not attending the day-to-day meetings. However, this privilege cannot be used for offenses (civil or criminal) that are punishable by more than six months, eg. rape, murder. In People vs. Jalosjos, the respondent who was found guilty of rape and in detention was not freed on his claim of popular sovereignty and the need of his constituents to be represented. Rather, it was ruled that for crimes punishable by a penalty of more than six years, the members of the Congress are not exempted from detention.
Privilege of Speech and Debate
This privilege enables the legislator to express views in the interest of the public without fear of accountability to support his statements with the usual evidence required in the court of justice. There are however two requirements in order that this privilege be availed. First, the remarks must be made while the legislature is in session; and second, they must be made in connection with the discharge of official duties. The Supreme Court declared in Jimenez vs. Cabangbang, that the privilege cannot be invoked by a legislator who had allegedly maligned the plaintiff in an open letter to the President of the Philippines coursed through and published in the newspapers. The finding was that he had written the letter at a time when the Congress was in recess and in his private capacity only. (Cruz, 2002)
photo sources: xenophilius.wordpress.com and wikipedia.com