Hundreds of workers at a manufacturing facility in Delta that makes parts for planes found themselves locked out of their jobs Tuesday morning, according to their union.

The International Association of Machinists and Aerospace Workers said the employer, Avcorp Industries, served a lockout notice to the union members around 10 p.m. Monday.

"Some people were caught by surprise here that the employer decided to escalate to locking them out in an attempt to get a deal," Walter Gerlach with the IAMAW told CTV News.

It's believed the lockout affects about 300 employees. Many of the workers build plane parts like wings and flaps for major aerospace companies like Boeing and Bombardier.

Employees on the picket line said it likely wouldn't take long for those companies to notice issue with supply.

According to the union, contract negotiations with the company started in January, while the contract itself expired in April.

There were mediated negotiations in August that stalled, IAMAW said. Since then, Gerlach says workers had started an overtime ban and had also started rotating job action about four weeks ago.

Avcorp Industries said it served the lockout notice as a "last resort" due to the impact of the rotating strikes.

"While Avcorp has endeavoured to remain open and continue production, unfortunately Avcorp is now at a point where it is unable to carry on its operations due to the continuing interruptions caused by these rotating strikes," it said in a statement to CTV News.

The company said it is "very close" to reaching a deal with the union, with terms of wages and benefits already mostly agreed upon.

Gerlach with the union said one of the main issues at the bargaining table is around changes to seniority recall rights for workers who had been laid off.

"Those changes have negatively impacted about 200 people who were laid off when there was a downturn and now there’s an upswing. And those people lot their seniority rights. They had to come back to the workplace without seniority and start at the bottom of the pay scale as well," Gerlach said. "They are wanting to have that language changed so they aren’t affected by that in the future again."

In response, Avcorp said current recall periods are "very generous" and capping of these rights is a commonly accepted industry practice.

The two parties also cannot see eye-to-eye on sub-contracting.

While Gerlach said the union is pushing to keep jobs local and not contracting them out, the company says "the union wishes to change the status quo and add more restrictions on Avcorp’s ability to reasonably and competitively manage its operation," it said.

Avcorp said it is working to reaching a collective agreement as soon as possible to get the "plant fully up and running again and getting employees back to work."