WARSAW (Reuters) - Polish legislators asked a court on Wednesday to detain the former CEO of oil refiner Orlen Daniel Obajtek to force him to testify on June 7 before a parliamentary commission investigating the country's cash-for-visas scandal.

The request came after Obajtek missed a second scheduled appearance before the panel that is probing claims officials under the former government of the Law and Justice (PiS) party accelerated visa applications for migrant workers in return for payments.

Obajtek, a candidate for PiS in the European Parliamentary elections on June 9, has been asked to appear because of Orlen's reliance on migrant workers to expand its petrochemical plant in Poland, though the panel has not suggested wrongdoing.

Obajtek has said the company's contractors were in charge of bringing foreign workers to Poland.

"I would like to submit a motion to impose a fine on the witness and to order the witness' detention and a warrant for compulsory appearance on June 7," the panel's chief and Civic Platform legislator Michal Szczerba said after Obajtek's second absence on Wednesday.

Asked by private broadcaster Polsat News on Wednesday evening whether he would appear on June 7, Obajtek said "I am not ruling it out... but I'm not saying I will come."

"I'm not afraid, but you have to know that one has to spend two days preparing for such a commission and be in Warsaw practically for one day. Those are three days taken out of the electoral calendar at the last moment of the elections, when one should be among people and campaigning," he said.

He added that he had asked Szczerba to postpone his hearing until after the June 9 election to the European Parliament (EP).

Szczerba is also running in the elections but in a different constituency.

Prime Minister Donald Tusk said on Wednesday he had no doubt Obajtek would appear in court, but added he would not exert pressure on prosecutors.

"There are enough determined people there to bring these people to court in the end, in accordance with the procedures and their professional decency," Tusk told reporters.

"I will not hurry prosecutors, judges or policemen in their work".

Prosecutors in Poland are also investigating the loss of about $400 million by Orlen's Swiss unit in prepayment for oil it didn't get, a potential fuel price manipulation and financial terms of Orlen's merger will smaller peer Lotos under Obajtek's helm. Obajtek has denied any allegations of wrongdoing.

(Reporting by Marek Strzelecki, Pawel Florkiewicz, Anna Wlodarczak-Semczuk and Karol Badohal; Editing by Jan Harvey)