BOSTON — Many school buses here had delayed arrival times or were no-shows last week as some schools opened early while the drivers union negotiates a new contract.

Boston Public Schools buses ran late or had not shown up to pick up students last Tuesday through Thursday for schools that started early — mostly independent charter schools, according to Boston Globe.

There are concerns that the problem could worsen as school officially starts on Thursday, the newspaper reports.

The district had struggled with an unexpected number of driver absences, and bus drivers were negotiating with Transdev, the district’s transportation contractor, to replace an agreement that was set to expire on Friday, according to Boston Globe.

The bus drivers union had raised the possibility of a walkout in June, the newspaper reports, when it unanimously voted to authorize a strike as its contract was set to expire, but a two-month extension was worked out. Whether the drivers’ absences last week were connected to labor issues or are coincidental was unclear as of last week. Mayor Martin Walsh said at a ribbon-cutting ceremony in which he expressed frustrations over the problem and apologized to families, students, and schools, that he didn't think the issues were related, and that he plans to meet with the union soon, according to the newspaper.

The union blamed the problems that occurred last week on the contractor and Boston Public Schools’ use of an algorithm designed by MIT students and professors to consolidate bus routes. In a flyer released on Monday, the union claimed that Transdev didn’t hire a sufficient number of drivers over the summer, didn't maintain a pool of replacement drivers or train new drivers, and left 45 routes uncovered.

According to another flyer from Aug. 27, the bus drivers union is seeking a cost-of-living increase, affordable health care, disability coverage, and trained bus monitors for every bus, and is opposing bargaining proposals that include reducing allotted time for daily bus inspections and subcontracting.

The union and the contractor were expected to meet again on Tuesday, according to Boston Globe.  

The newspaper also reports that another issue driving the school district's transportation problems is the abrupt departure of its transportation director, John Roderick, who had previously worked for Transdev. The district told the newspaper that Roderick, who was hired earlier this year, left Aug. 24 and moved to New York City. Meanwhile, Delavern Stanislaus, the transportation department's customer service manager, is acting as interim director.