In a forceful statement outside Downing Street just hours after the European Union's negotiator set out his plans for the talks, May said some people in the EU did not want the process to succeed.
"In the last few days, we have seen just how tough these talks are likely to be," the Conservative leader said, charging that Britain's negotiating position had been "misrepresented" in the European press.
"The European Commission's negotiating stance has hardened. Threats against Britain have been issued by European politicians and officials," she said.
"All of these acts have been deliberately timed to affect the result of the general election that will take place on June 8."
May added: "The events of the last few days have shown that -- whatever our wishes, and however reasonable the positions of Europe's other leaders -- there are some in Brussels who do not want these talks to succeed. Who do not want Britain to prosper."
May called the snap election last month, saying she wanted a stronger mandate from voters ahead of the Brexit talks.
"Whoever wins on 8 June will face one overriding task: to get the best possible deal for this United Kingdom from Brexit," she said.
"If we don't get the negotiation right, if we let the bureaucrats of Brussels run over us, we will lose the chance to build a fairer society."
May made her comments after she visited the head of state Queen Elizabeth II to mark the dissolution of parliament ahead of the election.
Opposition Labour Party leader Jeremy Corbyn condemned May's comments, accusing her of "playing party games with Brexit" ahead of the election.
"By winding up the public confrontation with Brussels, the prime minister wants to wrap the Conservative party in the Union Jack and distract attention from her government's economic failure and rundown of our public services," he said.
Nicola Sturgeon, leader of the Scottish National Party, tweeted that May's comments "poison the atmosphere for partisan reasons", calling them "deeply irresponsible".
"Making a bogeyman of EU is all about distracting attention from the Tories' wider record -- while PM continues to hide from voters," she wrote.
