It is completely unconstitutional that businesses are forced to close on Sunday.
How so?
To do so establishes a State bias or support of a particular religion, Emsworth. Nothing could be more obvious.
Actually, no it doesn't, unless the law that forces businesses to close on Sunday states specifically that it is done so because some religions mandate a day of rest. Of course, you are more concerned with nonexistant religious bias than the fact that such a law would force an employer to do something that the government should not force him to do... that is where the invasion of freedom lies.