One of the functions of a Party Whip in the Legislature is to

The Party Whip is a member of a political party who is responsible for ensuring that party members in the legislature vote in accordance with the party's policies and decisions. One of their functions is to ensure that members are present during important sessions, such as when key votes are taking place. They may also be responsible for counting the votes of party members and enforcing discipline among them to ensure they vote in line with party directives. Therefore, the answer is: "ensure that members are present during important sessions."