Russian President Vladimir Putin, right, Jean-Claude Juncker in Moscow on September 25, 2012 | Yuri Kochetkov/AFP via Getty Images MEPs say Juncker’s Russia trip will ‘strengthen’ Putin Group of center-right politicians ask Commission president to reconsider the visit.

A group of MEPs from the center-right European People's Party said Wednesday that Commission President Jean-Claude Juncker should reconsider a trip to Russia planned for this month, claiming it will "strengthen" Vladimir Putin.

In an email obtained by POLITICO, six lawmakers, representing several countries, wrote to the leader of the EPP group in the European Parliament, German MEP Manfred Weber, asking him to raise the issue with Juncker. The Commission president this week confirmed plans to go to St. Petersburg on June 16-18 to take part in an international conference hosted by the Russian president.

It will be the first visit by the leader of an EU institution since sanctions against Moscow were introduced in March 2014 after the country’s incursions in Ukraine, including the annexation of the Crimean peninsula.

The MEPs wrote Weber that the visit, “at a time when Russia is continuing to blatantly ignore its commitments” under international law, “is inappropriate” since it “will strengthen Putin’s position and set a precedent for doing 'business as usual' with Putin’s regime while formally preserving the policy of sanctions.”

Officials said Juncker could still back out of the trip if Putin makes an unexpectedly provocative move.

The MEPs who signed the email were: Michael Gahler (Germany), Gunnar Hökmark (Sweden), Sandra Kalniete (Latvia), Tunne Kelam (Estonia), Cristian Dan Preda (Romania) and Jaromír Štětina (Czech Republic).

Weber's office declined to comment on the email.

An EPP source confirmed that Weber received the email but "he is not going to tell Juncker what to do."

On Monday, Estonian Foreign Minister Marina Kaljurand also questioned the value of Juncker's trip to Russia, but urged the Commission president to send a clear message to Putin.

"I expect him to relay clearly the European Union's common positions concerning EU-Russia relations, and first and foremost to call on Russia to meet its international obligations when it comes to European security and human rights, to end the aggression in Ukraine and the unlawful annexation of Crimea," she told the BNS news agency.

Juncker's spokesman Margaritis Schinas told reporters Monday that the Commission president would use the trip “to convey to the Russian leadership as well as to a wider audience the EU’s perspective regarding the current state of EU-Russia relations.”

Schinas did not say whether Juncker would meet privately with Putin, but told reporters “it would be evident that two leaders being there will have to meet because they will be there, attending the same forum.”

Officials said Juncker could still back out of the trip if Putin makes an unexpectedly provocative move or if the situation worsens on the ground in Ukraine.

The trip is not being billed as any kind of EU endorsement for Putin or his policies in Ukraine.

The EU is expected to prolong the sanctions against Russia that come up for renewal in July, even though some EU countries have wavered in their support for the measures, saying they hurt Europe’s agricultural and industrial sectors.

According to diplomatic sources, several countries — including the U.K. and the U.S. as well as some Baltic and Central European nations — have privately expressed unease that Juncker’s participation in an event clearly designed to burnish Putin’s credentials as a statesman could only bolster the Russian position at a delicate moment in the sanctions debate.

Juncker's planned trip to St. Petersburg is not being billed as any kind of EU endorsement for Putin or his policies in Ukraine. Schinas told reporters Monday that “we don’t see any inconsistency with the decision of the president to attend” the conference and the EU’s position on sanctions.

Maïa de la Baume contributed to this article.