House Democrats' campaign arm on Friday took an official step to protect sitting lawmakers, warning would-be campaign vendors that the party won't award contracts to political firms working for primary challengers.

With its new policy, posted Friday morning, the Democratic Congressional Campaign Committee (DCCC) said its "core mission" is to keep and grow the party's newly won House majority, "which includes supporting and protecting incumbents."

ADVERTISEMENT "To that end, the DCCC will not conduct business with, nor recommend to any of its targeted campaigns, any consultant that works with an opponent of a sitting Member of the House Democratic Caucus," the policy reads

The effort is an attempt to pre-empt a short but growing list of potential primary hopefuls, as well as the groups supporting them, from retaining the help of top-tier polling and consulting firms in bids to oust sitting lawmakers.

The liberal groups that supported Ocasio-Cortez and Pressley, and are now eyeing challenges to centrist incumbents this cycle, were quick to blast the DCCC's new policy on Friday, accusing the Democrats of using their financial muscle to stifle the energy of the surging liberal base.

"The DCCC is using financial leverage to try and stop leaders like Ayanna Pressley and Alexandria Ocasio-Cortez rising in the party through primary challenges," Alexandra Rojas, executive director of the Justice Democrats, a liberal advocacy group, said in a statement.

María Urbina, national political director of Indivisible, another liberal group, went a step further, saying the new hiring standards will discourage the political participation of minorities.

"This is another example of the DCCC looking to maintain the status quo and hoard power," Urbina said Friday. "This historic class of women, especially women of color, wouldn't have been ushered in if they'd waited their turn.

"This works to incentivize Congress staying white and male."

With an eye at avoiding that issue, the DCCC is also adopting new diversity standards for its vendors, which must demonstrate a commitment to empowering minorities to win a contract. Toward that end, vendors must meet one of five reported criteria, including having women, veterans or minorities in ownership roles or constituting a significant portion of the firm's staff. The aim is both to empower minorities in a field long dominated by white men and to ensure the vendors reflect the voters and candidates in the districts they're working to win.

Justice Democrats are already seeking a primary challenger to take on Rep. Henry Cuellar, a Blue Dog Texas Democrat, and they're eyeing races against other centrists around the country.

Newman told supporters this month that she's exploring another run in 2020.

"I would prefer that, as far as Democrats go, that we just work together, and we make sure that our colleagues can come back, and that we do what we can to pick up additional seats," she said in an interview from the party's campaign headquarters just off of Capitol Hill.

"Dan Lipinski is pro-life, but he's also a longtime member of the House of Representatives, and he's been a reliable vote on the vast majority of our issues," she added.

The DCCC's move to blacklist firms that serve primary challengers, they maintain, will only help Republicans.

"The Democratic Party establishment is sending a signal that they are more afraid of Ayanna Pressley and Alexandia Ocasio-Cortez winning primary challenges than Dan Lipinski or Henry Cuellar who votes with Trump nearly 70% of the time," said Rojas.

"The DCCC is trying to further entrench a consultant class that won’t challenge the big corporate donors and powers that are sitting at the top of the Democratic Party."

The DCCC's new policy ensures that any challenger, from the left or right, would face new obstacles to ousting incumbents. Aside from highlighting intraparty divisions during the primary season, such challengers have also created some tension between some veteran lawmakers and the newcomers who defeated their old colleagues.

"Look, she came last year. Campaigned against me. I beat her," he said Monday during a press event in his district. "And I’ve turned the page."

Updated: 4 p.m.