I am currently doing the same thing. I think its best to askt heir permission rather than them possibly seeing down the track, getting upset and then you have lost a client, at best a ruined relationship.
As a designer, we are always taught to ask when it comes to IP or logos/branding. Not only is it respectful and is ‘quality control’ for that business, but it also means that you can request files from the business with the right quality/no background etc. rather than do a stodgy job finding one on the internet that will appear pixelated or just not good to look at! If you’re not sure what specs you are asking for when you request the logo files, just tell them where you intend to put it (Website, pamphlet etc.) or usually their media/marketing team will just send you over a heap of different sized ones.
I also think it’s great to request it from the business as it opens up a new level of communication between the two of you, and shows you respect the brand.