South Oxfordshire Conservatives are accusing their Liberal Democrat colleagues on the district council of political sour grapes.
The claim follows moves by the Liberal Democrats to deny Conservatives an extra seat on the important scrutiny committee which monitors the work of the ruling cabinet.
A recent by-election in Watlington won by Conservatives made them the largest single party on the 50-strong council with 21 members.
But the Liberal Democrats, with 19 members, rule the council in a coalition with the seven Labour members. There are three Independents.
By law, committees have to reflect the political make-up of the council.
Officers said the Conservatives should have another seat on the scrutiny committee.
But the ruling groups rejected the move and cut the number of members on the scrutiny committee.
Conservative spokesman John Cotton said: "The voting was 23-23 in the full council meeting so the Liberal Democrat chairman decided it with his casting vote.
"It was an appalling example of political sour grapes."
Council leader and cabinet chairman Jan Morgan was not available for comment.
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