Toyota said in a statement that the plan unveiled late Friday discriminates "against American autoworkers based on their choice not to unionise."
The bill, set to be voted on Tuesday by the Democratic-led House Ways and Means Committee as part of a proposed US$3.5 trillion (RM14.5tril) spending bill, would benefit Detroit's Big Three automakers, which have union-represented auto plants.
In a statement, Honda called the bill "unfair" and said it "discriminates among EVs made by hard-working American auto workers based simply on whether they belong to a union. ... The Honda production associates in Alabama, Indiana and Ohio who will build our EVs deserve fair and equal treatment by Congress."
The proposal, estimated to cost US$33 billion to US$34 billion (RM141bil) over 10 years, would boost to up to US$12,500 (RM52,000) the maximum tax credit for electric vehicles, up from the current US$7,500 (RM32,000). The US$12,500 figure includes a US$500 (RM2,100) credit for using US-produced batteries.
The proposal is a key part of Democratic President Joe Biden's goal to ensure EVs comprise at least 50% of US vehicle sales by 2030 and boost American union jobs.
The bill, however, does away with phasing out automakers' tax credits after they hit 200,000 electric vehicles sold, which would make General Motors Co and Tesla Inc eligible again. It would also create a new smaller credit for used EVs of up to US$2,500.
GM, Ford Motor Co and Stellantis NV, the parent of Chrysler, assemble their US-made vehicles in plants represented by the United Auto Workers (UAW) union.
In contrast, foreign automakers operating in the United States as well as Tesla do not have unions representing assembly workers and many of them have fought efforts by the UAW to organise US plants.
Tesla would be eligible for up to US$8,000 credits under the bill.
UAW president Ray Curry said the tax credit provision "would go a long way in supporting-good paying union jobs in (the) EV auto sector that President Biden has championed."
The bill limits the EV credit to cars priced at no more than US$55,000, while trucks could be priced up to US$74,000.
Toyota added it will "fight to focus taxpayer dollars on making all electrified vehicles accessible for American consumers who can’t afford high-priced cars and trucks."