Legal action against the proposed closure of 29 local Post Office branches is being considered by Birmingham City Council.
A six-week consultation exercise concerning the closures is due to end on Wednesday.
The council has suggested it will seek a judicial review if the Post Office presses ahead with its plans.
But a spokesman for the Post Office said a legal challenge would be likely to fail.
Council leader Albert Bore said: "Cabinet were unanimous in their opposition to the proposals.
"We agreed that we would take whatever measures we can to get these plans dropped, even if that means taking our case to the High Court."
The cabinet's views and objections were also being forwarded to the Trade and Industry Select Committee, which is carrying out an inquiry into the proposals for the branches in the south of Birmingham.
A spokesman for the Post Office said the organisation was implementing government policy.
"I can't believe there are any grounds for a judicial review of the processes we have taken.
"We are implementing government policy, supported by government funding.
"There is no legal recourse available to the public if the Post Office decides to close a branch."