BNP secretary general Mirza Fakhrul Islam Alamgir has written to the Speaker requesting her to extend the time for taking oath.
He had written the letter before the 90-day deadline for an MP to take oath under constitutional obligations expired on Tuesday, local media reports say, citing the Parliament Secretariat.
Once the 90-day deadline ends, an MP-elect have the time extended with the Speaker's approval to take oath at a later date.
Earlier on Thursday, BNP MP-elect Zahidur Rahman (Thakurgaon-3) took oath amid warnings of tougher actions.
He was the first from the BNP to join parliament, only two days later to face expulsion for violating the party decision.
After his oath-taking, the BNP standing committee also held a series of meetings to keep the rest five MP-elects from joining the parliament.
Rumours had it already in the political circle that the BNP MPs-elect will take oath under a negotiation with the government for the party's chairperson Khaleda Zia's release.
A number of media outlets also ran reports regarding this. The BNP senior leaders, however, dismissed the reports.
Partly ending all the rumours and proving the reports, four other MPs-elect except Fakhrul took oath on Monday.
Fakhrul defended the oath-taking, saying that the party's MPs-elect were taking oatth upon instructions from the acting chairman, Tarique Rahman.