An investigation by Reuters found that more than 1,500 radical candidates are standing, many of them peddling anti-Western rhetoric and pushing for extreme religious laws to be applied across the country.
Western governments are particularly concerned as some of these are closely linked to terrorist organisations.
A total of 260 candidates have been put up by The Milli Muslim League, whose leader co-founded the group responsible for the brutal 2008 Mumbai terror attack which killed 166.
The extremist party Ahl-e-Sunnat Wal Jamaal is fielding dozens of candidates under a different name, despite being banned as the political wing of a terror group which targets Pakistan’s minority Shia Muslim population. The party denies the link.
A further 566 candidates are standing for Tehreek-e-Labaik Pakistan, a radical group which demands the death penalty for those who insult Islam.
A supporter of the group recently attempted to assassinate Pakistan’s interior minister, though the party denied responsibility.
Pakistan has been struggling with merciless terror groups since the US demanded they take action after the 9/11 attack.
Many of the extremist parties are also linked to Pakistan’s military and intelligence community.
Moved Yusuf, a top academic from the US Institute of Peace, told CNBC that as a result they “feel that their entry into politics has been blessed by elements within the Pakistani state apparatus”.
Wednesday’s vote is primarily being fought between parties led by former Prime Minister Nawaz Sharif and ex-cricket megastar Imran Khan.
However it will be difficult for either Mr Sharif or Mr Khan to form a majority government, meaning radical religious parties could play a role within a coalition Government.
Such an outcome could increase tension with the West, which is already furious at Pakistan over its alleged failure to contain terrorism.
Earlier this year the United States ended all military assistance to Pakistan until it deals with terror groups which are based on its soil.
In January President Trump threatened in a tweet to cut off all aid to Pakistan if terror groups continue to use the country as a safe haven.
The US has given Pakistan more than 33billion dollars in aid over the past 15 years.