SALZBURG, Austria — Poland broke ranks with the rest of the EU27 at a crucial ministers meeting on Brexit strategy this week, suggesting that the bloc's negotiating guidelines may need to be rewritten in October if a Brexit deal is still out of reach.

The intervention, at the General Affairs Council meeting of ministers in Brussels Tuesday was the first open threat of a serious crack in EU unity since the start of withdrawal negotiations with Britain. Polish Minister for EU Affairs Konrad Szymański did not receive support from anyone else at the meeting, but even the hint of defection from the EU27's common position suggests that the bloc's so-far rock-solid unity will come under increasing strain as the talks enter their final weeks and days.

Three diplomats present at the GAC meeting said that Poland proposed amending the Council's guidelines, which provide tightly scripted marching orders for the bloc's negotiator, Michel Barnier, "if the need arises in October."

“It's the only member state that expressed a very pro-U.K. position,” said one of the diplomats who attended the meeting. “It called for flexibility and if necessary to amend the guidelines,” the diplomat added. “That view was in total isolation.”

For months, London has pursued a strategy of attempting to bypass Barnier by appealing directly to EU capitals.

Hungary did not join in the call for more flexibility, but Viktor Orbán, the country's prime minister, declared at a separate summit in Salzburg, Austria, on Thursday that he was outside the "camp" of EU leaders who want to punish the U.K. over its decision to leave.

"I am very positive on Britain so I don’t like the approach to punish the British just because they decide to leave. It’s a great nation so we should have a fair approach ... we should like to have a fair Brexit," he said.

Whether Orbán acts on his rhetoric or not, senior EU leaders have long feared that other disputes within Europe — in particular its feud with Poland and Hungary over rule of law and democracy standards — could taint the Brexit process and diminish EU27 unity.

For months, London has pursued a strategy of attempting to bypass Barnier by appealing directly to EU capitals for more flexibility — so far without much tangible success. So the first signs of potential cracks in the EU's common position are highly significant.

“They have been trying all possible ways to break us, and they are good at that, but they have always failed,” a senior EU diplomat said last week.

The government in Warsaw, led by the Law and Justice party, has made no secret of its disdain for Brussels, and has bucked the EU establishment in the past, notably as the only country to oppose the reelection of Council President Donald Tusk.

Tuesday's General Affairs Council meeting provided an opportunity for Barnier to brief ministers ahead of an informal summit of EU leaders in Salzburg, Austria, where Brexit was the main topic of conversation at a leaders' lunch Thursday without U.K. Prime Minister Theresa May present. She made her pitch on Brexit in a 10-minute speech during dinner Wednesday evening.

Poland, which relies heavily on its military relationship with the U.K. and the U.S. as a deterrent against Russia, has already expressed a willingness to be more flexible than the rest of the EU27 in the Brexit negotiations.

Warsaw floated the idea that perhaps there is a need for more flexibility at a General Affairs Council meeting in July, but was quickly rebuffed by others. “We argued that the price we ask is already the right price,” one diplomat said.

Some diplomats said they do not believe Poland will escalate divisions but is rather seeking to send a public signal to Britain because of the large number of its nationals living there (an estimated 1 million, according to the U.K.'s Office for National Statistics.)

With so many of its nationals in the U.K., Warsaw has a crucial stake in making sure that a withdrawal treaty is agreed that will protect citizens' rights, including residency rights, after Brexit.

Poland is concerned about the impact of Brexit on its businesses.

One diplomat said Warsaw wants to offer as much flexibility as possible on the difficult issue of the Northern Ireland border so as not to scupper a deal on everything else. “They want to do everything possible on Ireland to get the solution for their citizens in the U.K.,” the diplomat said. “They just wanted to send a political message.”

Poland is also concerned about the impact of Brexit on its businesses. Earlier this month it warned of the "trade difficulties" that will stem from any kind of deal, and the potential for the talks to end in the "fiasco" of a no-deal scenario.

But other diplomats said Poland's isolation is a positive sign that the EU unity was intact. “The fact that nobody followed Poland: It's a further indication that unity is and remains strong," one diplomat said.

Polish officials did not reply to POLITICO's requests for comments.