Social-Democratic Party head Almazbek Atambayev said cabinet members had the right to be members of parties, and that President Kurmanbek Bakiyev's demand that ministers quit either the cabinet or their party was illegal.
Earlier Bakiyev gave ministers until April 13 to choose between their cabinet jobs and party membership, saying he did not want them to attend to party affairs at the expense of ministerial duties.
"Basic rights and freedoms include the right to unite," Atambayev said. "The Constitution says that no-one can have their right to belong ... to a union limited."
He said the law on state service should not restrict government official's rights and freedoms as citizens.
Bakiyev said earlier that cabinet members "should either suspend their party membership, following the example of Prime Minister Felix Kulov, or file a resignation [from the cabinet]. Combining both is unacceptable."
Kulov in April suspended his membership of the Ar-Namys party he had been leading since its foundation in 1999 to challenge then-president Askar Akayev.
Analysts say the measure is part of Bakiyev's efforts to eradicate corruption and tighten discipline in the government of the Central Asian republic. He won the presidency on an anti-corruption and democracy ticket last July, after serving several months as interim head of state following Akayev's overthrow in the "tulip revolution."
