"The unbridled imagination of the parties and their counsellors is without bounds," financial prosecutor Eliane Houlette told the court on the first day of the trial, which is due to last until 15 September. "It has transformed the legal battle into a guerrilla struggle."
Cahuzac's Swiss banker, François Reyl, launched a number of legal challenges to the charges of covering up tax fraud between the time the investigation started in 2013 and the decision to take it to court in 2015.
They amounted to the "exploitation of procedural rules for purely delaying tactics", she argued, calling on the court to reject them.
Reyl, Cahuzac's ex-wife Patricia Ménard, and his former lawyer Philippe Houman face associated charges and Reyl's bank is named in the prosecution.
The Cahuzac affair, in which the man charged with chasing up tax fraud was found to have hidden millions in a Swiss bank account himself, is the biggest scandal faced by President François Hollande's Socialist government.
It led to Cahuzac's resignation and disgrace and the establishment of a special financial crimes prosecutor's office, which Houlette is representing at the trial.