The announcements intensified a tense standoff over the drive for independence in the northeastern region, just over a week ahead of then contested vote scheduled for .
The conservative national government said it was launching an appeal at the Constitutional Court against the plan for a non-binding ballot on whether Catalonia should break away from the rest of Spain.
It had already forced Catalan president Artur Mas to water down his initial plan for an official referendum-style vote and now says even his amended plan is illegal.
Mas defied the government's latest appeal, saying it had "crossed the line into the realm of the ridiculous".
He vowed to press ahead with the vote.
"The central government is abusing its power and the law," Mas said in a speech on Friday. "It is using the Constitutional Court in an improper way. It is not the court's job to resolve political conflicts."
Mas had planned a kind of official non-binding referendum, but later downgraded it to a symbolic vote organised largely by volunteers.
He said the amended plan was legal and called on Catalans to vote on and "give a great lesson in democracy and civility".
"We will ask our legal services to study what legal action may be taken against the Spanish government for this abuse of power," he said.
Conservative Spanish Prime Minister Mariano Rajoy said that the vote did not respect "democratic conditions".
Proud of their distinct language and culture, Catalans have been demanding greater autonomy over recent years. The region of 7.5 million inhabitants accounts for nearly a fifth of Spain's economy.
But according to a poll published in top-selling daily newspaper El Pais, 49 percent of Catalans are against the watered-down referendum and 44 percent in favour.
The drive for the vote has put the moderate centre-right nationalist Mas in a tight spot, raising political uncertainty in the region.
Other Catalan parties have demanded a snap regional election if he fails to deliver on the planned referendum.
The Catalan Republican Left, which props up Mas's CiU group in the regional parliament, has said Catalans should declare independence unilaterally if parties can muster a majority in favour of such a move.
Rajoy is fiercely opposed to Catalonia breaking away from Spain and has vowed to defend the unity of the country as it emerges from an economic crisis.
He said he is open to "dialogue" to settle the standoff, but only by strictly legal means.