I only know about 上网 or 上线, that is, to go online the Internet. But 上纲上线 can be heard from time to time, but the speakers often cannot clearly define the meaning. Neither can I.
上纲上线 means raise common things (actions, opinions) at the level of big issues about nation, society, morals or politics.
A: 好啊, 你喜欢外国货是吗? 你怎么不买国货? 叛徒!
(A: Wow. You like foreign products? Why didn't you buy products made in our country? TRAITOR!)
B: 别上纲上线, 完全没道理.
(B:stop, that's nonsense.)
A: 我觉得不一定非要让座, 我也很累啊.
A: 你总是喜欢上纲上线, 让不让座跟素质有什么关系?
上纲上线 means treating a small issue (action or opinion) as a big issue like nationale and belief, as Jacob has answered.
I'd like to add that this is mostly used for objection to others' speeches or opinions, and has a negative meaning.
Even 上纲上线 is not spoken explicitly, there are some common phenomena and substitution expressions in China that has this meaning. For example when someone says he hates Huawei, others will blame that he's not a patriot. In this case, he can reply with "别上纲上线，不就是一部手机嘛。" (Don't overemphasize this. It's only (a matter of) a phone.)