Councillor Alan Lafferty has been named as the new deputy leader after Paul O’Kane was elected to Holyrood on the West Scotland list.
His appointment was confirmed at a meeting last week, where councillors urged council leader Tony Buchanan to push for extra representatives.
Councillor O’Kane will continue to serve until the council elections in May, but has stepped down from a number of roles, including education convener.
Councillor Gordon Wallace congratulated Councillor O’Kane, but said: “If ever evidence was needed as to how under-resourced we are as a council, it’s right there in front of us in Councillor O’Kane’s success at Holyrood.”
The number of East Renfrewshire councillors was cut from 20 to 18 for the 2017 election.
Councillor Wallace asked Councillor Buchanan whether “pressure can be brought to bear on the powers that be”.
He added: “Each councillor has an awful lot on their plates and everyone is trying to do the best that they can. I would ask the leader of the council to please voice our concerns.”
Provost Jim Fletcher echoed the concerns.
He said: “We did have all party unanimity to argue for more councillors rather than fewer and it was obviously a decision of the boundary committee.
“We would have needed to go down the road of judicial review and I don’t think there was much appetite to take the risk for that.
“What was disappointing for me, was the lack of support from our MSP colleagues from all the parties when it was debated at Holyrood.”
Councillor O’Kane said he would “do all I can now and in the future to raise that issue”.
Councillor Buchanan added: “I would suggest that we should probably have about 22 councillors to cover the population of the authority.
“Although there is no review scheduled for councillor numbers, I’m certainly more than happy to push the issue.
“The population is continuing to increase, that in itself should allow for an increased number of councillors, for increased representation.”
Councillor Barbara Grant said: “It’s very, very bad that we are in a situation where we don’t have enough people to do justice to what the community needs are.”