Boeing and the union representing striking machinists have negotiated a new contract proposal that would provide bigger pay raises and bonuses in a bid to end a costly walkout that has crippled production of airplanes for more than a month.

The International Association of Machinists and Aerospace Workers said early Saturday that it plans to hold a ratification vote Wednesday.

The union said the deal would increase pay by 35% over four years, up from 30% that was offered last month. It also boosts upfront bonuses to $7,000 per worker instead of $6,000.

The new offer would not restore a traditional pension plan — a key demand of the 33,000 striking workers — but it would increase the amount of contributions to 401(k) retirement plans that Boeing would match, the union said.

“We look forward to our employees voting on the negotiated proposal," Boeing said in a statement.

About 33,000 members of IAM District 751 began a strike on September 14. The strike has halted production of Boeing 737s, including the 737 Max, and 767s and 777s. Boeing is continuing to build 787 Dreamliners at a nonunion plant in South Carolina.

The strike has led new Boeing CEO Kelly Ortberg to announce about 17,000 layoffs and take early steps toward raising up to $25 billion from new stock or debt to bolster the company's finances.