Just one week into her congressional tenure, freshman Rep. Alexandria Ocasio-Cortez is ruffling feathers within her own party — which is now mounting a behind-the-scenes effort to rein in the social media star.

Democrats have expressed concern about the Bronx-born socialist, mostly over her backing of a campaign by Justice Democrats to mount primary challenges against the party’s moderates.

The leftist group behind the push announced its first “primary target,” Rep. Henry Cueller, on Friday in a tweet calling him a “fake Democrat” and putting out the call for a “grassroots progressive challenger.”

Two of Justice Democrats lead organizers now work for Ocasio-Cortez in Congress — as her chief of staff and head of communications.

So far, the youngest woman to serve in Congress hasn’t won everyone over with her outspokenness.

“I’m sure Ms. Cortez means well, but there’s almost an outstanding rule: Don’t attack your own people,” Rep. Emanuel Cleaver (D-Mo.) told Politico. “We just don’t need sniping in our Democratic Caucus.”

Politico spoke to nearly 20 Democratic lawmakers and aides who said there’s a two-fold effort from within to rein in Ocasio-Cortez — warning that she could wind up isolating herself, but also trying to harness her star power to unite the party in its fight against Republicans.

Some Democratic leaders are also annoyed that Ocasio-Cortez slammed the House’s new “pay-go” provision — requiring that all new spending be paid for by either increasing taxes or by budget cuts — on Twitter.

Meanwhile, the rank and file don’t appreciate the push to get her appointed to a top committee position that they think she doesn’t deserve.

Other legislators worry that the social media darling, who has been dubbed “AOC” and has 2.28 million Twitter followers, isn’t using her star power wisely.

“Her use of social media and attention that she commands for an institution like this could create some unease,” Rep. Nydia Velázquez (D-NY) told The Post. “But at the same time we need to know and understand that the challenges that we are facing require us to be focused and proactive.”

Fellow Democrats have kept their criticisms of Ocasio-Cortez to themselves, fearing she could sic her millions of Twitter devotees on them with a single tweet.

But Velázquez is stepping in to try to bring the 29-year-old into the fold — and convince fellow Democrats to appreciate what she adds to the party.

“She brings the passion, new energy and bold ideas and I think that the Democratic Party will benefit out of what she brings and we need to be open and listen to her and learn,” Velázquez said. “One area is how masterful she has been with social media. A lot of us, we need to learn and be more proactive in engaging our constituents.”

She added, “We shouldn’t be afraid of the fact that she has 2 million followers.”