© Reuters / Albert Gea
Court sources have said the details of the case against Mas are being finalized and will probably be filed on Thursday, Reuters reports.
Although the independence vote was informal and non-binding, it saw 2 million out of a possible 5.4 million people take part, in which 80 percent voted for independence.
Mas hailed the vote as "a great success" but it immediately drew harsh criticism from the Spanish government.
Justice Minister Rafael Catala dismissed it as "a sterile and useless sham" and "a day of political propaganda."
Comment: Oh, put a sock in it, Catala! You're the sham. If you're lucky enough to even be remembered, you'll go down in history as the villain here, along with all the other sterile and useless Spanish politicians blocking the self-determination of the Catalonians.
However, Prime Minister Mariano Rajoy says he wants to open up dialogue with Mas.
On Tuesday, Mas said he is keen to start discussions over Catalan independence and other measures to help the economy of the region, which accounts for about a fifth of Spain's economic output and population.
And while Rajoy has said he will never agree to a legal vote on independence for Catalonia, he has said that he may budge slightly on reforming the constitution to give the Catalans some powers of their own on spending and taxation.
Isn't this the usual 'test'? If leadership succumbs to such low level pressure, it demonstrates how weak it really is. Perhaps Mr. Mas should return the favor?