US aircraft manufacturer Boeing has made an improved offer to thousands of striking workers, including a 38% pay rise over four years, the IAM trade union said on Thursday. The trade union’s 33,000 members at Boeing will be asked to vote on the proposal on Monday. The offer comes seven weeks into a strike at Boeing. Last week, workers overwhelmingly voted down an offer of a 35% pay raise over four years, with 94% rejecting the proposal. In mid-September, they had already rejected the first Boeing offer, which included a 25% pay increase, by a majority of almost 95%. The latest proposal also in…