Courts have made it harder for workers to prove certain discrimination claims over the past decade. Now, a bipartisan group of lawmakers is trying to reverse course.

Legislation that’s been marketed as protecting older workers from discrimination would help a broad range of workers suing their employers over bias on the job, but it has an uphill battle in Congress, law professors and attorneys told Bloomberg Law.

Dubbed the “Protecting Older Workers Against Discrimination Act,” the bill re-introduced earlier this month would lower one hurdle that workers must overcome to prove that employers engaged in age or disability discrimination, or...