Petroineos, the only crude oil refinery in Scotland, has cut the percentage of biofuel in its diesel after the NFU Scotland complained about fuel problems affecting hundreds of its members.
The union says more than 400 members have reported fuel issues such as clogged filters and breakdowns.
Petroineos said it was investigating and had recently reduced the biofuel inclusion percentages - from 7% down to 5% - in the hope of alleviating any problems.
The company said it had allocated “significant resource” to investigate the issues since they came to light in October.
In a statement it said: “Our investigations have been extensive and are ongoing into what is a complex process with a large number of variables.
“We recognise the need for action to ensure that end-users do not experience further unnecessary operational issues.
“We remain entirely focused on providing quality fuel to the markets we serve. We are monitoring the effectiveness of the changes we are making.”
NFU welcomed the decision by Petroineos to reduce biofuel content as being a short-term solution to be complemented by the creation of an expert working group set up in order to put long-term measures in place to prevent this issue from reoccurring.
However, it said an immediate priority is the problem that many farmers have fuel in storage on farms associated with breakdowns, and it is working to get commitment from stakeholders to support farmers in the recovery of this fuel.