Two Senate committees will investigate the alleged budget irregularities.
Senator Juan Ponce Enrile, chairman of the committee on finance, said he only wanted to "satisfy the public and the opposition."
"The impression is that there is something illegal, sinister, malicious and covetous in all of these things. We have to clarify that," he told reporters.
In his privilege speech on Monday, Mr. Lacson directly implicated Senate President Manuel B. Villar, Jr. in what he called "road to nowhere" mess.
But this early, Mr. Enrile noted nothing was irregular about the insertions. "There are no illegal insertions. In fact, you cannot spend any money in the budget unless you comply with the procurement law on public bidding," he told reporters in a chance interview.
Senator Ramon B. Revilla, Jr., chairman of the committee on public works, told BusinessWorld, "I welcome [the investigation] since we have to ferret out the truth cannot speculate at the moment" if there was any irregularity.
In a related development, Senator Joker P. Arroyo said Mr. Lacson allegations were unfounded and that he will oppose any investigation.
"If we investigate, we admit that we engaged in corruption," he said in a briefing, adding Mr. Lacson "twisted" the facts and "obscured the whole thing."
"Is he [Mr. Lacson] saying that [Congress] is wrong and he is the only one right? The sanctity of the proceedings in the Senate is at stake here. This is serious because this is the first time in the history of the Senate that a member challenged the Senate," Mr. Arroyo said in response to Mr. Lacsonâ€™s accusations that corruption was "committed right in this hall [Senate]."