Sandwell Council's Labour leader Kerrie Carmichael turned down a request to appoint Conservative councillors in leading positions on scrutiny committees, saying her own party would ensure "a full compliment of experience".
Tory councillors said they were "disappointed but not shocked" by the decision, and accused Labour of lacking transparency.
Scrutiny committees play a key role on local authorities, allowing councillors to hold the ruling cabinet to account and question decisions.
Under the council's previous Labour leader, Rajbir Singh, the Tories say they were given leading roles on two committees, namely children's services and education, and economy, skills, transport and environment.
Conservative councillor David Fisher said: "I’m disappointed but not shocked. Labour say the right things but we’re returning to the closed doors and dodgy deals of the past.
"We’re the second largest group on the council. And it’s important different voices are heard throughout the council process.
"But with this decision, Labour councillors will be marking the homework of other Labour councillors."
After the latest round of local elections Labour has 61 councillors to the Conservatives' 10.
Responding to a request from the Tory group regarding scrutiny roles, Councillor Carmichael said she had "decided that we will not be asking the opposition to take any positions this year".
She added: "We have reshuffled scrutiny chairs and vice chairs this year ensuring a full compliment of experience."
Councillor Carmichael told the Express & Star the Conservatives had been offered "at least one or two places" on each of the authority's five scrutiny boards, and had also been offered positions on other key council panels.
"These boards are also open to the public so there is extra opportunity to observe," she added.