Sena, an NDA ally led by Uddhav Thackeray, however, maintained it will not field nominees against BJP's Prime Ministerial aspirant Narendra Modi and party president Rajnath Singh, contesting from Varanasi and Lucknow respectively.
Sena's decision to contest in the most populous state, which sends 80 MPs to Lok Sabha, comes in the backdrop of a section of Maharashtra BJP making overtures to MNS chief Raj Thackeray, Uddhav's estranged cousin and rival, for some sort of poll-related arrangement to avoid a split in saffron votes.
"We have our alliance with BJP in Maharashtra, not in Uttar Pradesh. We will strive to expand our party in other parts of the country. Shiv Sena will field 20 candidates in Uttar Pradesh," Sena spokesman Sanjay Raut told reporters.
He did not name the seats from where Sena will contest.
Meanwhile, the BJP said it has old ties with its trusted alliance partner and they would achieve success in the Lok Sabha elections in Maharashtra by bagging the maximum seats.
BJP chief Rajnath Singh asserted that if there are "any shortcomings in the alliance, we can resolve through talks".
"I can vouch with confidence that the relations of BJP with Shiv Sena cannot break at any cost. If there are any shortcomings in the alliance, we can resolve through talks," he said in Delhi.
BJP is making heavy political investment in Uttar Pradesh and fielding Modi from there is part of a strategy to maximise its electoral gains from that state.
"We will not field candidates from Varanasi and Lucknow," Raut told PTI.
Sena is miffed ever since BJP leader Nitin Gadkari met Raj early this month to reach an understanding to consolidate anti-Congress votes. However, the meeting did not yield anything significant.
The party will also contest the Lok Sabha elections in Bihar (5 seats) and Delhi (7 seats) besides Punjab, West Bengal and Kerala, said Raut.
When parties like JD (U), Trinamool Congress, DMK and AIADMK can come from outside and fight polls in Maharashtra, why can't the Sena do the same in other States he asked.
"Shiv Sena is one of the oldest parties in the country. It is a big party. We have our strength," Raut added.