The protests are related to a bonus that Vale wasn't able to pay after plunging commodity prices cut into earnings, Bloomberg reports. Vale claims that it isn't required to pay the profit-sharing bonus since the union signed a labor accord.
The Rio de Janeiro-based metals and mining company didn't reveal how output was impacted by the protests, Bloomberg adds.
Union president Sebastiao Alves de Oliveira is meeting with union leaders to determine whether to continue strikes on Wednesday.
Vale is scheduled to report 2015 fourth quarter earnings before the market open on Thursday.
Separately, TheStreet Ratings team rates the stock as a "sell" with a ratings score of D.
Vale's weaknesses include its disappointing return on equity, weak operating cash flow, generally disappointing historical performance in the stock itself and feeble growth in its earnings per share.
You can view the full analysis from the report here: VALE
TheStreet Ratings objectively rated this stock according to its "risk-adjusted" total return prospect over a 12-month investment horizon. Not based on the news in any given day, the rating may differ from Jim Cramer's view or that of this article's author.