GEORGETOWN, Sept. 25 -- Bauxite workers in Guyana may strike on Monday if a three-month wage dispute remains unresolved, possibly affecting shipments of the aluminum ore from the South American nation, a union said.

Guyana is the fourth-largest supplier of bauxite to the United States. The union wants higher pay and better terms from German transporter Oldendorff Carriers, which ships out between 2.0 million and 2.5 million tonnes of the ore each year.

Oldendorff Carriers employs more than 100 people in the country, where it has operated since 2006 under an 11-year deal with Russian aluminum giant UC RUSAL (0486.HK: Quote)(RUAL.PA: Quote), which runs Guyana's bauxite mines through a subsidiary.

Leslie Gonsalves, head of the Guyana Bauxite and General Workers Union, accused Oldendorff on Friday of refusing to negotiate on issues including unpaid bonuses.

"These acts are not only in violation of local laws but also international labor conventions that every employer, local and multinational, is bound to obey," the union said in a statement.

Oldendorff officials could not immediately be reached for comment.