The Electrical Contractors' Association, which represents more than 2, 000 firms countrywide, says the hold-ups have caused chaos for apprentices, employers and colleges alike.
Delays by the exam body in issuing the results of its 2360 Certificate examinations in electrical installation left some trainees having to sign on at colleges to take the second part of the course without knowing whether they had passed the first stage.
In the meantime, they had to wait for substantial pay increases due on passing the first-year exams.
The ECA, whose member firms currently all put their trainees through City Guilds qualifications, has formally complained to the exam body over the delay, which it says affected 2,500 apprentices employed by its members alone.
The apprentices sat the exams in June, but their results were not available until September - the longest delay ever to have affected the qualification.
City Guilds blamed the problems on computer difficulties, and claimed every effort had been made to ensure results were released as early as possible.
But the ECA, which says the time taken to process the data in recent years "has never been really satisfactory", insists it is considering turning to another exam body, or may even devise its own qualification.
A spokesman said apprentices had suffered "embarrassment and annoyance" after registering to take the next stage of a course only to find they had failed the previous one.
Employers could now be faced with bills from colleges for students applying for a second-year course which they then do not take, he said.
For colleges, the delay had led to problems estimating student numbers for the present year and in calculating exam successes for the previous one, he added.
First-year apprentices, who are usually school-leavers, are paid only Pounds 56.25 a week, but the figure increases to Pounds 94.50 once they pass their first stage exams. After passing the second stage, weekly pay rises to Pounds 139.50.
City Guilds admitted the results of this year's part one exams had been hit by "unusual and unforeseen delays", and said the issue of the certificate results was being addressed "as the highest priority".
But the exam body's own guidance still states that processing of some exam papers can take an average of eight to ten weeks.
One London college is still waiting for the results for one third-year examination taken in June, leaving students in difficulties as they apply for jobs or further study. Results for other courses also came in late, or with some names missing.
A college spokesman said the worst delays would have a knock-on effect on December resits, because students must be registered to retake the exams by the end of this month.