According to The Election Commission Act of 1991 “The Commission may appoint observers to supervise, inquire or monitor the act of polling, counting of votes, or any other act of election.”
In 2008 Constituent Assembly Elections, according to the Election Commission’s Election Observation Resource Center, 147 domestic organizations with, in total, 92,000 individual observers, have registered to observe the process. In addition to the domestic organizations, international groups from the European Union, Carter Centre, Asian Network for Free elections (ANFREL), Asia Foundation, Socialist International, the Universal Human Rights Network , and several embassies and other organizations have also applied to send international observers. According to the EORC, there may be as many as 600 international observers in total, making this election one of the most observed in recent history.
In 2013 Constituent Assembly Election, according to Carter Center’s election report, 31,654 domestic (citizen) observers from 46 organizations and 249 international observers from three organizations were accredited. In practice, citizen observers were able to observe most aspects of the process. However, legislation does not clearly define the rights of observers and opens the possibility for election officials to deny access to observers. For instance, the law is silent regarding the presence of observers at ECN meetings or at the printing of ballots, and the ECN did not allow observation of these activities by either citizen or international observers. The ECN directive on the election process stipulates that a maximum of five observers may be present in a polling center at any given time. Moreover, the law does not require returning officers to allow observers to be present in the counting centers but does not state the grounds for denying access. Carter Center observers noted that citizen observers were, on occasion, denied full access to polling and counting processes.
ECN rules also placed some undue restrictions on observers. For instance, citizen observers were required to be at least 21 years old and have specific educational qualifications. These requirements were more stringent than the requirements to become a voter and, therefore, impinged upon the right of some citizens to take part in the public affairs of their country. In addition, the educational qualifications discriminated against women and marginalized groups, which historically have lower levels of education.
Source
https://asiafoundation.org/resources/pdfs/NepalIntl.ObsManual.pdf
https://www.cartercenter.org/resources/pdfs/news/peace_publications/election_reports/nepal-2013-final.pdf