Some Express Scripts employees will soon vote on whether they want to be represented by District 837 of the International Association of Machinists.

The representation election is the result of growing employee discontent with wages, overtime and workplace favoritism, union officials said.

An Express Scripts spokesman said Wednesday the company has made workplace improvements in recent years, arguing union membership is not in the best interest of employees.

If the union receives a majority of the votes, it will represent about 300 employees who work as pharmacy technicians and clerks at Express Scripts’ headquarters in north St. Louis County, according to Michael Lloyd, a business organizer with IAM District 837, which also represents local Boeing employees.

The National Labor Relations Board confirmed it will conduct the secret ballot election on Oct. 14 and Oct. 18 at Express Scripts.

Lloyd said a previous attempt to organize failed in 2013. Express Scripts had made “promises” to stave off the union, Lloyd said, but those promises haven’t been kept, and employees again reached out to the union.

The employees earn between $11 and $13 per hour and work long hours, Lloyd said.