CANTON, Miss. (AP) — International unions supporting an effort to unionize Nissan's Mississippi assembly plant are questioning the automaker's sponsorship of the Olympics in Rio de Janeiro.

Brazilian union representatives delivered a letter to Rio organizers Thursday claiming Nissan Motor Co. violates committee guidelines stating workers have a right to bargain collectively.

Spokesman Philip Wilkinson says organizers received the letter.

The United Auto Workers wants to unionize the 6,300-worker Canton complex over company opposition. Nissan spokeswoman Kristina Adamski says the company respects national labor laws and allows workers to choose unions or not, noting the UAW has never sought a vote in Canton.

In December, the National Labor Relations Board said Nissan was violating Canton workers' rights by forbidding them to wear pro-union and anti-union t-shirts, and because a manager illegally threatened pro-union workers.