Morales' opponents say the bill, already partially approved, would give Morales political advantage because it assigns more seats to the poor, indigenous parts of the country.
But recent polls show Morales to be far ahead of his rivals for Bolivia's presidency, particularly amongst the Andean nation's indigenous majority.
He has championed their rights since he took office in 2006.
The main framework of the election bill, which supports indigenous Bolivians and sets a December 6 general election date for both presidential and congressional elections, was passed on Thursday.
However, congress must still approve the details.
Morales' party has enough votes to ratify the bill in the lower house and senate, but the opposition is refusing to give the quorum needed for a vote on the measure.
"Their plan is to stop the elections ... they know we can win with two-thirds of votes," Morales said.
He accused his rivals of being "racist, fascist [and] selfish".
Morales also said that he had received supportive phone calls from Hugo Chavez, the Venezuela president, and Fidel Castro, the former president of Cuba.
But in one concession to the opposition, Morales on Saturday ordered the compilation of a new electoral census after opposition politicians said Morales and his supporters could carry out vote-rigging.
Morales, a former coca farmer, has said he once went without food for 18 days in 1998 to protest against the then-government's policy on coca, the raw material for cocaine revered by Bolivian Indians for its medicinal and nutritional properties, Reuters reported.