"It would be difficult to stop the construction of the fourth nuclear power plant simply by issuing an administrative order," Jiang told reporters after a closed-door discussion with Su Tseng-chang, chairman of the Democratic Progressive Party (DPP).
The plant outside Taipei has been one of the most contentious projects in Taiwan over the past three decades.
The DPP opposes it on safety grounds while the ruling Kuomintang party says the island will run short of power unless it goes ahead.
The visit by Su came on the eve of a planned indefinite protest fast by Lin Yi-hsiung, who was DPP chairman from 1998-2000.
Lin, 72, has since early 2000 devoted himself to battling the island's nuclear power policy.
A group of his supporters urged fellow Taiwanese to rally behind the activist.
"Mr. Lin will stop taking food from April 22. The outcome of the action will be dictated not only by his resolve but by the determination of you and me -- masters of the country," it said in a statement.
Jiang urged Lin not to cause himself any harm.
The government agreed last year to hold a referendum on the new nuclear plant but it has failed to agree the terms of the vote with the opposition.
Anti-nuclear groups pledged to stage rallies and sit-in protests from Tuesday to try to halt the plant's opening. State-run Taiwan Power Co (Taipower) says it is 98 percent completed and due to come online in 2015.
Construction began in 1999 but the plant has been the subject of intense political wrangling ever since.
Concerns about the island's nuclear facilities have been mounting since 2011, when the Fukushima nuclear plant in Japan was hit by a tsunami which knocked out power to cooling systems and sent its reactors into meltdown.
Taipower currently operates three nuclear power plants.
Like Japan, the island is regularly hit by earthquakes. In September 1999 a 7.6-magnitude quake killed around 2,400 people in the deadliest natural disaster in the island's recent history.