In a statement released Thursday and obtained by Mindanews, Pimentel said he has asked Commission on Elections Chairperson Benjamin Abalos to relieve Tambuang.
Pimentel said he was informed that Tambuang allegedly instructed his subordinates "to pad the votes for Team Unity senatorial candidates. MindaNews tried to reach Tambuang, but Melcar Unso, regional Comelec spokesperson, said he was busy Friday.
Tambuang was sent to Lanao del Sur as part of a Comelec monitoring team watching the conduct of special elections there Saturday.
Unso told MindaNews that his office has not received any information regarding the senator's move.
Comelec Commissioner Romeo Brawner's chief of staff, Belen Carasig, told reporters Thursday that there was no cheating that happened during the canvassing of votes for the senatorial tally. He explained the controversy as "only a clerical error committed by personnel of the Commission on Audit (COA)".
"It was just an honest mistake," Carasig said.
The Davao City board of canvassers this week also made a similar explanation.
A recount of votes here was ordered by the Comelec over accusations of vote-padding and shaving and was finished Friday. The local Board of Canvassers would reconvene Saturday to present the results.
But questions have lingered on whether or not that what happened here was a case of failed vote padding or just a "clerical error" as the Commission on Elections and the local Board of Canvassers, chaired by lawyer Irma Vera Morcillo, insisted.
Pimentel claimed there was a clear plan to carry out "special operation" aimed allegedly at making it appear that eight Team Unity candidates won here and the rest of the region.
The Comelec has denied the allegation, with Brawner earlier saying that four personnel from the Commission on Audit working in the Board of Canvassers have already admitted the mistake and filed affidavits about the error.
Brawner's lawyer, Carasig, said that when they learned about the incident on May 22, Brawner immediately ordered the BOC for a recount. She said they found the errors from a preliminary investigation with those responsible "immediately owned the mistake."
She said the clerical errors did not only happen in Davao City, but also in the Visayas and Luzon.
But Carasig hinted the findings were not final and that they would also conduct an investigation.
Mayor Rodrigo Duterte, who pledged "the votes in Davao will be counted and be counted right" told reporters in a press conference Thursday that it was the camp of re-electionist senator and Team Unity bet Joker Arroyo who first called his attention, triggering a probe among lawyers from both opposition and administration slates.
The Board of Canvassers relieved four COA personnel working in the tabulation, after admitting they committed "clerical errors" in the tally.
Team Unity senatorial bets Sen. Ralph Recto and Ilocos Sur Luis Singson appeared to have benefited in the controversy, with increased votes attributed to double entry.
In the questioned tally, Recto ranked fifth when votes for Genuine Opposition bet Aquilino Pimentel III, about 84,236 was computed with the former's votes.
Pimentel's vote, however was not shaved, and was accounted to his total.
The same happened to GO candidate Sonia Roco's votes. Her votes were added to Singson's, bloating his total to 20,600, instead of just 14,573 votes.
There were also reported inconsistencies in the tally of opposition bet Antonio Trillanes IV whose tally was bloated by thousands of votes. The discrepancy, which Pimentel claimed was "vote-padding", did not just favor Team Unity bets.
Television reports showed that partial results from the recount as of Friday afternoon have Recto sliding down to 14th place.
Rector's lawyer, Aristotle Liwag, in a press release said the "inadvertent addition of votes" surprised them and called for a probe on the matter.
He denied their camp was involved and said it put the senator's candidacy in the bad light.