Pacquiao, who has won world titles in eight different weight divisions, is facing contempt charges for what the Bureau of Internal Revenue calls his refusal to provide documents relating to his sources of income and tax payments.
"I shall fight this case to the finish, until the last and final round," Pacquiao told a news conference in Manila. "I cannot train hard with this excess baggage."
Pacquiao is scheduled to fight Timothy Bradley in Las Vegas on June 9.
Elected congressman in 2010, the 33-year-old described the case against him as "plain and simple harassment" and said he was being singled out by the revenue agency.
"Over the years as a boxer, product endorser and businessman, I have not short-changed the government of what is due," he said.
He added that the tax agency had sent summons to the wrong person and the wrong address while he was fighting Juan Manuel Marquez last November.
Lawmaker Ralph Recto defended Pacquiao, saying he deserved to be treated better. "How much goodwill and pride has he given to the country?" he asked.
On Friday, Kim Henares, head of the revenue bureau, told foreign correspondents the case against Pacquiao was to compel him to submit 62 documents, including contracts for endorsement of products and services, and earnings from his fights and pay-per-view deals.
"Basically, they were given a lot of chances to present it and they still were not able to," Henares said, adding that Pacquiao's representative had been to the tax office but had not presented the documents.
She said the government would withdraw its contempt case against him once the documents had been submitted.
Henares added that the bureau began an inquiry into Pacquiao's tax records after it noted a huge drop in his tax payments in 2009. In 2008, he paid more than 50 million pesos but only 7 million the following year, she said.