Taiwan's main opposition party weighed in on the fight over a controversial plan to process the island's nuclear waste overseas Monday, calling for an immediate halt to the proposal.

Environmental activists say that the plan by state-run Taiwan Power Co (Taipower) to ship the waste abroad runs the risk of a nuclear accident and an international backlash from campaign groups.

Now the major opposition Democratic Progressive Party (DPP) has also pledged to shoot down the plan, accusing Taipower of a lack of transparency.

It comes as the government faces increasing pressure over its nuclear energy policy.

Taipower launched the bidding process for firms to transport and reprocess 1,200 spent fuel rods from two of the island's nuclear plants just before the Lunar New Year holidays -- a tactic opponents said was to evade media and public attention.

It also launched it before the budget was fully approved, the DPP said.

"The whole bidding process was not transparent," DPP legislator Tien Chiu-chin told AFP, warning that it could become a "money pit" and result in international disputes both environmentally and financially.

"Taipower must stop the public bidding immediately."

Tien added that the DPP would "do everything" to block the budget for the Tw$11.25 billion ($356 million) project, which still needs to be passed in parliament.

Companies from England, France and Russia have expressed interest in bidding for the proposal, local media reported.

Opponents have also accused Taipower of coming to a secret agreement with French company Areva over the waste plan.

Areva was "in negotiations" to process nuclear fuel from Taiwanese power stations in France, former Green MEP and anti-nuclear activist Didier Anger told AFP last month.

Taipower argues that it may have to shut down the two plants where the fuel rods are stored if the waste is not removed, as they are running out of capacity.

Safety concerns have mounted over Taiwan's nuclear facilities since 2011, when Japan's Fukushima plant was hit by a tsunami.

Like Japan, Taiwan is regularly hit by earthquakes.

Last year the authorities were forced to seal off a new power plant due to open in 2015, pending a referendum on its future.

But the government says Taiwan will run out of energy if it ditches nuclear power altogether -- the three plants currently operated by Taipower supply about 20 percent of the island's electricity.

Taipower has said the technology to reprocess spent fuel is mature and that countries including Germany, Japan and Italy have shipped their nuclear waste overseas for reprocessing.