Generally, your employer cannot require you to "work for free." However, there are many, many caveats to that, including your membership in any one of a dozen or more professional designations. Moreover, if your employer is requesting that you simply make up the time you were late at the end of the day, that does not seem unreasonable.
Try and look at the situation objectively: are you putting in the usual 40 hours in the week? If so, I think you can relax. If you are putting in more time than that, then I urge you to think about the value of your employment to you. I am available to discuss off-line at no cost on Monday.