The cust could mean that as many as 20,000 people could lose their jobs.
Any retrenchment by Ford in the US would expose the carmaker to risk of more criticism from Donald Trump.
The carmaker has around 30,000 salaried workers in the US. Fields has been pouring billions into electric autos, self-driving cars and ride-sharing experiments as its conventional vehicle business has struggled more so than crosstown rival General Motors Co. amid a slowing USA market. The source requested anonymity in order to be able to discuss the matter freely.
The cuts could be announced as soon as this week, the WSJ said.
In a statement given to the AP, Ford said its priorities are reducing costs and improving efficiency.
Ford plans to emphasize the voluntary nature of the staff reductions. Fields has said Ford will cut costs by about $3 billion this year and that earnings will rebound in 2018.
While Ford has been profitable since Fields became CEO in July 2014, shares have fallen by about a third over that period. The small cars that were to be built there will now be built at another Mexican plant.
Since taking office Trump has made it a top priority to boost the United States carmaking sector.
With sales heading lower, job cuts by automakers and the much-larger auto parts ecosystem seemed likely after being a leading source of new manufacturing employment in recent years.
Ford in February, announced it would acquire artificial-intelligence startup Argo AI with plans to invest $1 billion over the next five years to expand the firm.
"Major investment to be made in three MI plants", Trump posted on Twitter. While many employees have been added to support higher volumes and expansion in global markets, Mr. Fields has also been hiring to support new technology ventures that fall outside of the company's core business of building and selling cars.