US aerospace giant Boeing has made an offer to tens of thousands of striking factory workers, including pay raises of 35% over the course of four years, the IAM trade union said on Saturday. The trade union’s 33,000 members at Boeing will be asked to vote on the proposal on Wednesday. The offer comes a month into a strike at Boeing. The new offer was negotiated with the support of US Labor Secretary Julie Su, according to the trade union. The proposal also provides for a one-off payment of $7,000 as well as improvements to retirement and sickness leave benefits. Boeing has also agreed to rever…