The lawmakers demanded that SRC reinstates Sh5,000 sitting allowance for every plenary session and car grant where every MP received a brand new car at the start of every Parliament.
Speaking during the induction workshop for the 13th Parliament, MPs reminded Ms Mengich that they are entitled to a plenary sitting allowance because they at times sit beyond the hours prescribed by the commission.
But the SRC chair was adamant that sitting allowance had not been abolished but was included in the MPs' consolidated pay which stands at Sh710,000.
She told the MPs that the commission arrived at their job evaluation through a scientific process which was fair and objective.
"Your basic pay of Sh710,000 takes into account all the functions that are discharged in line with the constitutional provisions of oversight, representation and law making," Mengich said.
"It includes what you do in plenary sessions, committee meeting and even visiting your constituency. It's all an inclusive pay that speaks to the entire role," she added.
SRC's tough stance may have come as a major shock for the MPs who have been pushing to have the allowances reinstated.
National Assembly Speaker Moses Wetang'ula had on Monday during the first day of the induction assured the MPs they will not lose the privileges their predecessors enjoyed.
The speaker, who is also the chairman of the Parliamentary Service Commission (PSC), said they were in talks with SRC with a view to rescind the decision to scrap allowances.
When they emerged to address the media, Wetang'ula was the first to disown what he had said only two days earlier. First, he told journalists that while the meeting had discussed many things, the remuneration of MPs was not one of them.
"No such thing was ever discussed," he said in comments that appeared to roll back his own words two days earlier.
"We had a fruitful debate on the mandate of the two institutions and the expectation of the MPs. It ended in a cordial manner. We discussed the role of SRC and Parliament and the way it can Help Kenya move forward in terms of people getting value for their labour."
But Mengich stuck to the script, insisting that the meeting had not agreed, or disagreed, on anything.
"The main objective was to introduce the MPs to the role of the SRC and mainly the basic principles we use to determine their salaries," she said.
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"Of course the issue of their pay came up. But there was nothing for us to agree or disagree on. It was an induction course. But we have heard their concerns and we shall engage with the commission as is normal and issue a communication," she added.
The MPs are unhappy with the Sh150,000 recently introduced as housing allowance. They said SRC was merely playing politics with their salaries as they had split their administrative pay to baptise it as house allowance.
In the last Parliament, the lawmakers received Sh284,000 as an administrative allowance. But MPs argue that SRC had split the amount into house allowance of Sh150,000 and Sh134,000 as salary adjustment a move they termed a con game.
Another contentious issue was mileage allowance and decision by SRC to cap the vehicle capacity to 3000cc.
While the legislators insist they should be allowed to use vehicles exceeding 3000cc, SRC has rejected it on account that it will push the mileage allowance beyond the required limit.
The MPs had also wanted the previous rate of Sh187.5 per kilometre in mileage claims to continue applying as opposed to the Sh119 gazetted by the SRC in its latest review.
Going for cars with big engine capacity means that MPs will claim more allowance.
The MPs said they come from places with different terrain and questioned the rationale of being lumped into the same category.
Mengich gave in to their demands for the car grant, saying it is an administrative issue that they will discuss with PSC
MPs from Nairobi, Naivasha, Machakos, Kiambu and Makueni have been grouped in zone A whose mileage is between 0-351 kilometers. They will be paid Sh116 per kilometre covered. For MPs in Group category B, mostly from far-flung areas, mileage claims will start from 351 kilometers to infinity and will be paid similar amounts per Sh116 per kilometre.