Two years after a bruising battle with unions, Fiat Chrysler Automobiles Chief Executive Sergio Marchionne is again butting heads with workers at his company's Italian factories, reported The Wall Street Journal.

Mr. Marchionne on Thursday canceled plans to shift 500 furloughed workers from a mostly idle Fiat plant in Turin to a nearby Maserati factory, according to a person familiar with the situation. Fiat has also shelved plans to use overtime at the same Maserati factory to meet booming demand for the luxury brand, the person said.

The executive's decision comes a few days after 200 workers belonging to the Fiom metalworkers union held a one-hour strike at the Maserati factory to protest general working conditions. The strike led to 11 fewer cars being built, Fiat said.

The strike at the Maserati plant was "incomprehensible, irrational and unjustified," Mr. Marchionne wrote in a letter published in Turin's La Stampa newspaper. "The recent episodes, the result of the actions of a small minority, caused a loss in production in a very delicate moment and can't be taken lightly."

Fiom couldn't be reached for comment.

Fiom has historically been the most combative of Italy's three main metalworkers unions and was the only one of the three not to sign a national contract that came into effect at the beginning of 2012. While the other two large metalworkers unions, Fim and Uilm, have calmer relations with Fiat, they have in recent weeks also raised their voices because the national contract expired at the end of December and hasn't been renewed.

Fim and Uilm chose not to strike on Monday. But in addition to the lack of a new contract, they are at loggerheads with Fiat over a one-off payment that is to be made to all workers. The company and the unions have agreed in principle to the payment, which comes in a year that salaries have been frozen, though they disagree on the amount. The unions initially asked for €390 ($529), while the company offered €200. Fiat has come up to €250 and the unions down to €300, though they haven't reached an agreement.

"Negotiations must restart so we can clarify with Fiat what has emerged in the last few hours," Federico Uliano, Fim's national secretary, wrote in a statement. "We haven't received anything written about the agreement [to shift the workers and make use of overtime] being revoked, so for us that agreement is still valid."

Uilm also hasn't received official word from Fiat, but several members working in the Maserati factory had been informed of the company's decision, said Eros Panigalli, Uilm's national secretary. He also called on Fiat to begin serious negotiations on renewing the national contract.