(Reuters) -Starbucks and its union representing more than 10,000 baristas have agreed to bring in a mediator to help resume stalled contract negotiations and reach a deal, they said in a joint statement on Thursday.

Talks between the two parties, which began in April last year, were halted in December before a final round, with the union saying the coffee chain had yet to bring a comprehensive package to the table.

"We have made progress over the last nine months of bargaining, and we are committed to continuing to work together - with a mediator's assistance - to navigate complex issues and reach fair contracts," said the joint statement, which was seen by Reuters.

Starbucks had said in December it scheduled and attended more than eight bargaining sessions with union delegates and reached 30 agreements.

The union, which has filed more than 90 unfair labor practices against the company in recent weeks, had gone on a five-day strike just ahead of Christmas, which closed Starbucks stores in multiple cities, including Los Angeles, Chicago and Seattle.