Voting for BN in the coming Permatang Pauh by-election means supporting the implementation of the goods and services tax by the federal government, Chief Minister Lim Guan Eng said today.

"This choice has to be made by the people - a vote for Umno is a vote for BN and a vote for GST and 1MDB," Lim said after a press conference today to announce the 50 year anniversary celebrations of the Penang Museum.

His position follows the criticism of Prime Minister Najib Razak's leadership by remark by former prime minister Dr Mahathir Mohamad.

Mahathir, who has launched a series of salvos against Najib recently, said supporting Najib is similar to supporting the financial mismanagement in the prime minister's pet project, 1Malaysia Development Bhd (1MDB).

Lim said the BN would also be using various strategies to deflect from the situation in Kedah, where Mahathir's son, Menteri Besar Muhkriz Mahathir, has been told to resign if he fails to show support for Najib.

"So the rakyat has to decide which party can address their problems, which party fights against the GST and 1MDB.

"Do not involve the people in the Umno crisis in Kedah. Let the people decide who is the best candidate to vote for," he added.

Lim said this in reference to Deputy Prime Minister Muhyiddin Yassin's visit to kick-start the Permatang Pauh by-election campaign ahead of its nomination day on April 25.

The Election Commission has fixed May 7 as polling day and May 3 for early voting.

'Umno united to wrest the seat'

During his press conference, Muhyiddin said Umno was united in facing the campaign to wrest the parliamentary seat from PKR.

He added that despite Umno being an "underdog" in Permatang Pauh, a PKR stronghold, "nothing is impossible".

Lim said from Muhyiddin's comment in Permatang Pauh yesterday, he gathered that the by-election would be a challenging one.

"I advise my friends in Pakatan not to be over-confident. We will give our support to PKR.

"It looks like we have a 50-50 chance to win the elections," Lim said.

"We are launching our Pakatan by-election machinery tomorrow but it seems BN has beaten us to it by doing it yesterday."

The seat held by PKR de facto leader Anwar Ibrahim was declared vacant after his family failed to seek his pardon on the Sodomy II conviction from the Yang di-Pertuan Agong.

Anwar began serving his five-year jail sentence in the Sungai Buloh Prison on Feb 10.

The PKR candidate for the Permatang Pauh seat s most likely to be his wife and PKR president Dr Wan Azizah Wan Ismail.