Toyota sent a letter to its British staff on June 20, jointly signed by Britain's biggest union Unite, warning of the economic consequences of the country leaving the European Union.
Ahead of Thursday's referendum on British EU membership, Toyota said it wished to clarify "misrepresentation" of its position by Leave campaigners which the company "strongly" objects to.
While holding back from urging staff and union members to vote for Remain, the letter warned of "significant business challenges" should vote to leave Britain leave the 28-nation bloc.
Toyota said "free access to the European Market is of critical importance" for its UK operations.
"Nearly 90% of all our vehicles (made in the UK) are exported and 75% of all our vehicle production is made for our customers in the EU," it added.
Toyota has two factories in Britain employing more than 3,400 people.
Earlier this year, British industry body the Society of Motor Manufacturers and Traders revealed that three-quarters of its members believed staying in the EU was best for business.
Political opinion polls put the contest at neck-and-neck, although financial markets and betting firms have Remain as the clear favorite.
Copyright Agence France-Presse, 2016