Hi, my first thought when I saw these dungarees was they were approx 1990s, but a classic style such as this can be hard to date.
The Lee company has been around since 1889. I looked at the company history and, if you scroll down, it does mention in 2017 the 'launch of Lee vintage modern' - but I would expect modern jeans to have care labels, as they are required by law.
https://eu.lee.com/uk-en/history.ht...Q4MTY4NC4xLjAuMTcyNTQ4MTY4NC4wLjAuNDYyNjkxMjE.
The AFL-CIO union label helps a bit in that it puts these dungarees as post 1955 (when the American Federation of Labor and the Congress of Industrial Organizations merged).
I found this USPTO Trademark, which looks (from what I can see) like your label. If it is the same, this helps may help narrow the date further.
I'm not great at understanding all the TM blurb, but here's the info;
1977-12-01 Date of First Use
1979-05-21 Application Filed
1982-06-08 Published for Opposition
1982-09-07 Trademark Registered
1989-04-07 Cancelled
1989-04-07 Status: Dead/Cancelled
1994-05-21 Location: FILE DESTROYED
2018-07-07 Transaction Date
https://uspto.report/TM/73216356
I'm not as familiar with US care labels as I am with those in the UK but, from my basic understanding, affixed care labels (text based), weren't required by law in the US until the early 70s. So these jeans may well be 70s, if there aren't any. It's hard to tell from the photos, but do the branded 'Lee' buttons have signs of wear/signs of age?