The Islamic republic, which insists its nuclear program is purely peaceful, started building the plant inside a mountain in secret as early as 2006, to protect it from air strikes.
Last week, Reuters reported world powers were planning to offer to ease sanctions barring trade in gold and other precious metals with Iran in return for steps to shut down Fordow.
Alaeddin Boroujerdi, head of parliament's national security and foreign policy committee, referred to the reported offer on Sunday and dismissed any idea of a closure, the Iranian Students' News Agency reported.
"Fordow will never be shut down because ... our national duty is to be able to defend our nuclear and vital centers against an enemy threat," Boroujerdi was quoted as saying by the agency.
"This suggestion (shutting down Fordow) is meant to help the Zionist regime (Israel)," he added.
Israel has threatened to attack Iran if diplomacy and sanctions fail to curb its nuclear program, raising fears of a regional war.
The United States and its allies are particularly worried about Fordow because Iran is refining uranium there to a fissile concentration of 20 percent, which Iran says it needs for a medical reactor. Twenty percent purity is only a short technical step from weapons-grade uranium.
Western officials said last week the offer to ease sanctions barring gold and other precious metals trade with Iran would be presented at February 26 talks between Iran and world powers in Almaty, Kazakhstan.
They acknowledged it represented a relatively modest update to proposals that the six major powers put forward last year.
Iran's parliament has little control over the Islamic Republic's foreign policy, which is decided by Supreme Leader Ayatollah Ali Khamenei.