Sacrilege is a noun meaning the misuse or desecration of something sacred. Sacrilegious is the corresponding adjective. The words are commonly misspelled sacrelige and sacreligious. Though sacrilegious things are often against religion, sacrilegious and religious have different roots. The similarity in sound is coincidental. Sacrilege comes from the Latin sacer (meaning sacred) and legere (meaning to gather), and religion comes from the Latin religio.
If you have trouble remembering how to spell sacrilegious, just remember that the e and first i in religious are reversed.
Examples
Sacrilege
And then the presentation is treated as if it were the Gospel and to change one word of it would be a sacrilege. [Forbes]
It seems like sacrilege to reduce beer into a simple syrup for the purpose of creating a second beverage. [Toronto Sun]
Sacrilegious
Nor would many Japanese see anything silly or sacrilegious in this unprecedented exercise in putting manga, as comics are known here, on a level with sacred art. [Financial Times]
[I]t seems verging on sacrilegious to doubt Federer’s ability to add to his grand slam tally. [Sydney Morning Herald]