The United Auto Workers (UAW) union is seeking a new election at a Mercedes-Benz vehicle plant in Alabama after losing a vote there last week, according to a petition filed on Friday with the National Labor Relations Board (NLRB).

The union accused Mercedes of engaging “in a relentless anti-union campaign” including the firing of employees who were pro-union and holding frequent captive-audience meetings to spread anti-union views, according to the filing.

“We sincerely hoped the UAW would respect our team members’ decision. Throughout the election, we worked with the NLRB to adhere to its guidelines and we will continue to do so as we work through this process,” a Mercedes spokesperson said.

The UAW lost when about 56% of the nearly 5,000 workers at the Vance, Alabama, plant and nearby battery factory voted against unionizing.

The defeat just over a week ago came amid the UAW’s ambitious union-organizing campaign to recruit 150,000 non-union auto workers around the US, and after riding a historic win last month at a Volkswagen plant in Chattanooga, Tennessee, where the UAW won a landslide victory with 73% of workers voting to unionize.

The UAW in its new filing said Mercedes’ efforts to influence the vote constituted unfair labor practices and prevented a free choice by employees, warranting a new election.

A spokesperson for the NLRB said a regional director will review the union’s objection and could decide to call for a hearing in the coming weeks.

The fight at Mercedes was much more contentious than at VW, where the company took a neutral stance, the union and labor experts said of US union relations with the management of the two rival German vehicle brands.

For example, Mercedes leaders frequently pointed to signs inside the plant urging employees to vote no, according to workers and photos reviewed by Reuters.

Mercedes also replaced the chief executive of its US business in the weeks leading up to the vote and encouraged employees to give him a chance, which some workers said added strength to the anti-union campaign.

Southern states have for decades successfully fought off unionization drives in an attempt to keep down labor costs – a practice critics have called the “Alabama discount”.