It is certainly not ideal and they would be better off in a controlled climate but if that isn't possible, heck, playing in the league is the most important thing and some bosses just do not understand when the golf bag is sitting next to the work desk (or as I was told by a friend). I think it also matters as to where you are and how extreme the conditions. Here in the Phoenix area in the summer, the grips would likely melt off and for sure the epoxy would give way on the shafts. Unfortunately, putting them in the back seat with the window cracked would have worked in 1960 but these days, your clubs would be gone within a week. Do what you must and good luck with that league. I used to really enjoy the one we had back in my working days in Texas.

Short answer - yes. A hot car is hard on the epoxy.

The 2012 US Women’s Open at Blackwolf Run was over 100 every day. I was a volunteer. On Day 3 I was on the Irish Course and launched the 8 iron head about 35 yards. Further than the ball went. Shudda kept the clubs in the hotel room instead of the trunk.
If you only have the clubs in the car on league day and the temp is no more than maybe 90, not ideal but probably ok.

As mentioned in some other responses, I'd worry about the grips first and foremost if you're in a southern climate.

I agree with everyone else that it’s a lil dangerous. I live in San Antonio and it is over 100 about 3 months outta the year. Also our area is now infamous for teenagers pulling door handles and breaking into cars. I don’t even leave mine in the garage. Do what you gotta do though.

I'm not sure how well this idea would work for you but I had a buddy who said it has worked for him.

His clubs were in the back of his car.
He had several reusable gel ice packs in the freezer at his office.
Once the temperature would start to climb, he would take his clubs out of the bag and wrap the grips and heads with a thin towel.
The he would put the frozen gel packs around the grips and heads
He would then check on them at lunch or afternoon and switch out to fresh ice packs if necessary.

Overkill in my book but I respected the effort.

Under the circumstances, I would say the trunk on play day only is ok. I leave mine in the garage, which is the same as leaving them in bag storage at the club, as bag rooms are generally not climate controlled.

Thanks everyone. Appreciate the responses. Looks like my babies will be sitting at my desk with me. It might make it harder to make the silent escape a tad early, but worth a shot

Be careful. I did that last year and it became too much of a distraction. My boss said that my work load was suffering so I needed to make different accommodations.
Too bad. I'm gonna really miss that job!!!