The White House's timetable for a decision on auto tariffs is being pushed back, the Wall Street Journal reported Tuesday.

Commerce Secretary Wilbur Ross had told reporters last month that a report on the implications of auto tariffs and their possible national security threat, would be published sometime in August.

But in a Journal interview published Tuesday, Ross said now it's "not clear the report will be out at the end of the month" and declined to set a new timeline. He said the report was being delayed because of ongoing negotiations with Mexico, Canada, and the European Commission.

Ross also said it was taking longer than anticipated to go through materials submitted by automakers, who are largely against tariffs that critics say would drive up costs to consumers and to their own supply chain.

President Trump has said could impose 20 or 25 percent tariffs on auto imports. He asked the Commerce Department in May to look into whether vehicle imports threaten national security, which is the same argument the White House used to impose steel and aluminum tariffs.

The U.S. has also imposed 25 percent tariffs on $34 billion in Chinese goods, and tariffs on steel. China has retaliated with its own tariffs, including a 40 percent tariff on cars.

Washington has been criticized by automakers and foreign governments as it considers tariffs of up to 25 percent. Critics have warned auto tariffs could boost the cost of cars, and hurt auto sales and jobs in the global industry. Tariffs would hit companies including Germany's BMW, Korea's Hyundai, Japan's Toyota as well as global factories for U.S. brands General Motors, Ford Motor, and Fiat Chrysler.

— Read the entire Wall Street Journal report here.