The government "will create an even more serious, extraordinary situation by seizing Catalonia's political autonomy," he wrote in a letter to the Spanish senate.
The senate is poised to approve measures on Friday to take away Catalonia's powers.
Puigdemont said that would be an "affront" to Spain's constitution.
In the senate, the central government is preparing to invoke the never-before-used Article 155 of the constitution which allows it to intervene in Catalonia.
Prime Minister Mariano Rajoy's conservative government plans to use this article to strip Puigdemont and the rest of his executive of their political powers. It also plans to take control of Catalonia's regional police force, public broadcaster and parliament.
Those measures are intended to last for up to six months, until regional elections are called and a new Catalan parliament is sworn in.
Spain's senate, where Rajoy's Popular Party has a majority, will convene Friday to formally approve measures under Article 155.
Puigdemont said the measures would violate "the principle of political autonomy" of Spain's regions. He added that the constitution does not give the central government blanket powers.
The Spanish constitution states Spain is "indivisible". But Puigdemont's separatist government declared itself "above" the constitution when it held an independence referendum on October 1.
That vote istelf was ruled unconstitutional by the courts.
The Catalan parliament is scheduled to meet Thursday afternoon to formulate a response to Madrid.
